Methods and compositions for nucleic acid analysis

ABSTRACT

The present invention is directed to methods, compositions and systems for analyzing sequence information while retaining structural and molecular context of that sequence information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/263,532, filed Dec. 4, 2015, which is hereby incorporated byreference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

Polynucleotide sequencing continues to find increasing use in medicalapplications such as genetic screening and genotyping of tumors. Manypolynucleotide sequencing methods rely on sample processing techniquesof the original sample, including random fragmentation ofpolynucleotides. These processing techniques can provide advantages interms of throughput and efficiency, but the resultant sequenceinformation obtained from these processed samples can lack importantcontextual information in terms of the location of particular sequenceswithin the broader linear (two-dimensional) sequence of the originalnucleic acid molecule that contained those sequences. Structural contextwithin the three dimensional space of the original sample is also lostwith many sample processing and sequencing techniques. There is thus aneed for sequencing technologies that retain structural and molecularcontext of the identified nucleic acid sequences.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides methods, systems andcompositions for providing sequence information that retains bothmolecular and structural context of the originating nucleic acidmolecule.

In some aspects, the present disclosure provides methods of analyzingnucleic acids while maintaining structural context. Such methods includethe steps of: (a) providing a sample containing nucleic acids, where thenucleic acids comprise three dimensional structures; (b) separatingportions of the sample into discrete partitions such that portions ofthe nucleic acid three dimensional structures are also separated intothe discrete partitions; (c) obtaining sequence information from thenucleic acids, thereby analyzing nucleic acids while maintainingstructural context.

In some embodiments, the sequence information from obtaining step (c)includes identification of nucleic acids that are in spatial proximityto each other.

In further embodiments, the sequence information from obtaining step (c)includes identification of nucleic acids that are in spatial proximityto each other.

In still further embodiments, the obtaining step (c) providesinformation on intrachromosomal and/or interchromosomal interactionsbetween genomic loci.

In yet further embodiments, the obtaining step (c) provides informationon chromosome conformations.

In further embodiments, prior to separating step (b), at least some ofthe three dimensional structures are processed to link differentportions of the nucleic acids that are in proximity to each other withinthe three dimensional structures.

In any embodiments, the nucleic acids are not isolated from the sampleprior to the separating step (b).

In any embodiments, prior to the obtaining step (c), the nucleic acidswithin the discrete partitions are barcoded to form a plurality ofbarcoded fragments, where fragments within a given discrete partitioneach comprise a common barcode, such that the barcodes identify nucleicacids from a given partition.

In further embodiments, the obtaining step (c) comprises a sequencingreaction selected from the group consisting of: short read-lengthsequencing reactions and long read-length sequencing reactions.

In some aspects, the present disclosure provides methods of analyzingnucleic acids while maintaining structural context that include thesteps of (a) forming linked nucleic acids within the sample such thatspatially adjacent nucleic acid segments are linked; (b) processing thelinked nucleic acids to produce a plurality of ligation products,wherein the ligation products contain portions of the spatially adjacentnucleic acid segments; (c) depositing the plurality of ligation productsinto discrete partitions; (d) barcoding the ligation products within thediscrete partitions to form a plurality of barcoded fragments, whereinfragments within a given discrete partition each comprise a commonbarcode, thereby associating each fragment with the linked nucleic acidfrom which it is derived; (e) obtaining sequence information from theplurality of barcoded fragments, thereby analyzing nucleic acids fromthe sample while maintaining structural context.

In some aspects, the present disclosure provides methods of analyzingnucleic acids while maintaining structural context that include thesteps of: (a) forming linked nucleic acids within the sample such thatspatially adjacent nucleic acid segments are linked; (b) depositing thelinked nucleic acids into discrete partitions; (c) processing the linkednucleic acids to produce a plurality of ligation products, wherein theligation products contain portions of the spatially adjacent nucleicacid segments; (d) barcoding the ligation products within the discretepartitions to form a plurality of barcoded fragments, wherein fragmentswithin a given discrete partition each comprise a common barcode,thereby associating each fragment with the linked nucleic acid fromwhich it is derived; (e) obtaining sequence information from theplurality of barcoded fragments, thereby analyzing nucleic acids fromthe sample while maintaining structural context.

In some aspects, the present disclosure provides methods of analyzingnucleic acids while maintaining structural context that include thesteps of (a) cross-linking nucleic acids within the sample to formcross-linked nucleic acids, wherein the cross-linking forms covalentlinks between spatially adjacent nucleic acid segments; (b) depositingthe cross-linked nucleic acids into discrete partitions; (c) processingthe cross-linked nucleic acids to produce a plurality of ligationproducts, wherein the ligation products contain portions of thespatially adjacent nucleic acid segments; (d) obtaining sequenceinformation from the plurality of ligation products, thereby analyzingnucleic acids from the sample while maintaining structural context.

In any embodiments, the sample is a formalin-fixed paraffin sample.

In any embodiments, the discrete partitions comprise beads. In furtherembodiments, the beads are gel beads.

In any embodiments, the sample comprises a tumor sample.

In any embodiments, the sample comprises a mixture of tumor and normalcells.

In any embodiments, the sample comprises a nuclear matrix.

In any embodiments, the nucleic acids comprise RNA.

In any embodiments, the amount of nucleic acids in the sample is lessthan 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 ng/ml.

In some aspects, the present invention provides a method of analyzingnucleic acids while maintaining structural context, in which the methodincludes the steps of: (a) providing a sample that contains nucleicacids; (b) applying a library of tags to the sample such that differentgeographical regions of the sample receive different tags or differentconcentrations of tags; (c) separating portions of the sample intodiscrete partitions such that portions of the library of tags andportions of the nucleic acids are also separated into the discretepartitions; (d) obtaining sequence information from the nucleic acids,and (e) identifying tags or concentrations of tags in the discretepartitions, thereby analyzing nucleic acids while maintaining structuralcontext.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a schematic illustration of molecular context andstructural context in accordance with the methods described herein.

FIG. 2 provides a schematic illustration of a process described herein.

FIG. 3 illustrates a typical workflow for performing an assay to detectsequence information, using the methods and compositions disclosedherein.

FIG. 4 provides a schematic illustration of a process for combining anucleic acid sample with beads and partitioning the nucleic acids andbeads into discrete droplets.

FIG. 5 provides a schematic illustration of a process for barcoding andamplification of chromosomal nucleic acid fragments.

FIG. 6 provides a schematic illustration of the use of barcoding ofnucleic acid fragments in attributing sequence data to their originatingsource nucleic acid molecule.

FIG. 7 provides a schematic illustration of an exemplary samplepreparation method.

DETAILED DESCRIPTION OF THE INVENTION

The practice of the present invention may employ, unless otherwiseindicated, conventional techniques and descriptions of organicchemistry, polymer technology, molecular biology (including recombinanttechniques), cell biology, biochemistry, and immunology, which arewithin the skill of the art. Such conventional techniques includepolymer array synthesis, hybridization, ligation, phage display, anddetection of hybridization using a label. Specific illustrations ofsuitable techniques can be had by reference to the example herein below.However, other equivalent conventional procedures can, of course, alsobe used. Such conventional techniques and descriptions can be found instandard laboratory manuals such as Genome Analysis: A Laboratory ManualSeries (Vols. I-IV), Using Antibodies: A Laboratory Manual, Cells: ALaboratory Manual, PCR Primer: A Laboratory Manual, and MolecularCloning: A Laboratory Manual (all from Cold Spring Harbor LaboratoryPress), Stryer, L. (1995) Biochemistry (4th Ed.) Freeman, New York,Gait, “Oligonucleotide Synthesis: A Practical Approach” 1984, IRL Press,London, Nelson and Cox (2000), Lehninger, Principles of Biochemistry3^(rd) Ed., W. H. Freeman Pub., New York, N.Y. and Berg et al. (2002)Biochemistry, 5^(th) Ed., W. H. Freeman Pub., New York, N.Y., all ofwhich are herein incorporated in their entirety by reference for allpurposes.

Note that as used herein and in the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a polymerase”refers to one agent or mixtures of such agents, and reference to “themethod” includes reference to equivalent steps and methods known tothose skilled in the art, and so forth.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. All publications mentionedherein are incorporated herein by reference for the purpose ofdescribing and disclosing devices, compositions, formulations andmethodologies which are described in the publication and which might beused in connection with the presently described invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges is also encompassed within the invention, subject to anyspecifically excluded limit in the stated range. Where the stated rangeincludes one or both of the limits, ranges excluding either both ofthose included limits are also included in the invention.

In the following description, numerous specific details are set forth toprovide a more thorough understanding of the present invention. However,it will be apparent to one of skill in the art that the presentinvention may be practiced without one or more of these specificdetails. In other instances, well-known features and procedures wellknown to those skilled in the art have not been described in order toavoid obscuring the invention.

As used herein, the term “comprising” is intended to mean that thecompositions and methods include the recited elements, but do notexclude others. “Consisting essentially of” when used to definecompositions and methods, shall mean excluding other elements of anyessential significance to the composition or method. “Consisting of”shall mean excluding more than trace elements of other ingredients forclaimed compositions and substantial method steps. Embodiments definedby each of these transition terms are within the scope of thisinvention. Accordingly, it is intended that the methods and compositionscan include additional steps and components (comprising) oralternatively including steps and compositions of no significance(consisting essentially of) or alternatively, intending only the statedmethod steps or compositions (consisting of).

All numerical designations, e.g., pH, temperature, time, concentration,and molecular weight, including ranges, are approximations which arevaried (+) or (−) by increments of 0.1. It is to be understood, althoughnot always explicitly stated that all numerical designations arepreceded by the term “about”. The term “about” also includes the exactvalue “X” in addition to minor increments of “X” such as “X+0.1” or“X−0.1.” It also is to be understood, although not always explicitlystated, that the reagents described herein are merely exemplary and thatequivalents of such are known in the art.

I. OVERVIEW

This disclosure provides methods, compositions and systems forcharacterization of genetic material. In general, the methods,compositions and systems described herein provide methods of analyzingcomponents of a sample while retaining information on the structural aswell as molecular context of those components as they were originally inthe sample. Although much of the discussion herein is in terms of theanalysis of nucleic acids, it will be appreciated that the methods andsystems discussed herein can be adapted to apply to other components ofa sample, including proteins and other molecules.

Deoxyribonucleic acid (DNA) is a linear molecule, and as such the genomeis often described and assessed in terms of linear dimensions. However,chromosomes are not rigid, and the spatial distance between two genomicloci need not always correspond to their distance along the linearsequence of the genome. Regions separated by many megabases can beimmediately adjacent in 3-dimensional space. From the standpoint ofregulation, understanding long-range interactions between genomic locimay be useful. For example, gene enhancers, silencers, and insulatorelements may possibly function across vast genomic distances. Theability to retain both structural and molecular context of sequencereads provides the ability to understand such long-range interactions.

By “retaining structural context” as used herein means that multiplesequence reads or multiple portions of sequence reads are attributableto the original three-dimensional relative location of those sequencereads within the sample. In other words, the sequence reads can beassociated with a relative location within the sample with respect toneighboring nucleic acids (and in some situations associated proteins)in that sample. This spatial information is available through themethods discussed herein even if those neighboring nucleic acids are notphysically located within the linear sequence of a single originatingnucleic acid molecule. Referring to the schematic illustration in FIG.1: in a sample (101), sequences (104) and (105) are located within thelinear sequence of two different originating nucleic acid molecules((102) and (103) respectively), but are located in spatial proximity toeach other within the sample. The methods and compositions describedherein provide the ability to retain that information on the structuralcontext of sequence reads and thus allow reads from sequences (104) and(105) to be attributed to their relative spatial proximity within theoriginal sample on the original nucleic acid molecules (102) and (103)from which those sequence reads are derived.

The methods and compositions discussed herein also provide sequenceinformation that retains molecular context. “Retaining molecularcontext” as used herein means that multiple sequence reads or multipleportions of sequence reads may be attributable to a single originatingmolecule of a nucleic acid. While this single molecule of a nucleic acidmay be of any of a variety of lengths, in preferred aspects, it will bea relatively long molecule, allowing for preservation of long rangemolecular context. In particular, the single originating molecule ispreferably substantially longer than the typical short read sequencelength, e.g., longer than 200 bases, and is often at least 1000 bases orlonger, 5000 bases or longer, 10,000 bases or longer, 20,000 bases orlonger, 30,000 bases or longer, 40,000 bases or longer, 50,000 bases orlonger, 60,000 bases or longer, 70,000 bases or longer, 80,000 bases orlonger, 90,000 bases or longer, or 100,000 bases or longer, and in somecases up to 1 megabase or longer.

In general, the methods described herein include analyzing nucleic acidswhile maintaining structural and molecular context. Such analysesinclude methods in which a sample containing nucleic acids is provided,where the nucleic acids contain three dimensional structures. Portionsof the sample are separated into discrete partitions such that portionsof the nucleic acid three dimensional structures are also separated intothe discrete partitions—nucleic acid sequences that are in spatialproximity to each other will tend to be separated into the samepartition, thus retaining the three-dimensional information of thatspatial proximity even when later-obtained sequence reads are fromsequences that were not originally on the same individual originatingnucleic acid molecule. Referring again to FIG. 1: if sample 101,containing nucleic acid molecules 102 and 103 and 106, is separated intodiscrete partitions such that subsets of the sample are allocated intodifferent discrete partitions, it is more likely that nucleic acidmolecules 102 and 103 will be placed in the same partition with eachother than with nucleic acid molecule 106, because of the physicaldistance between nucleic acid molecule 106 and 102 and 103. As such,nucleic acid molecules within the same discrete partitions are thosethat were in spatial proximity to each other in the original sample.Sequence information obtained from nucleic acids within the discretepartitions thus provides a way to analyze the nucleic acids, for examplethrough nucleic acid sequencing, and attribute those sequence reads backto the structural context of the originating nucleic acid molecules.

In further examples, the structural context (also referred to herein as“geographical context”) may be maintained by using tags (such as barcodeoligonucleotides) to encode the geography of the sample. In somesituations, this can include injecting a viral library encoding acollection of barcoded sequences (such as mRNA sequences) to a sample.The barcodes travel through the sample by active processes or bydiffusion. When the sample is then further processed in accordance withmethods described herein and known in the art, barcodes can becorrelated with structural positions to identify nucleic acid sequencesfrom the same geographic location within the sample. In examples inwhich the barcodes are distributed through the sample through activeprocesses, sequences with the same barcode may be geographicallyconnected and/or connected through the same process. As will beappreciated, this system of using tags to encode structural context canbe used alone or in combination with methods described herein utilizingdiscrete partitions to further retain structural and molecular context.In examples in which tags for encoding spatial locations and barcodesfor identifying molecules separated into the same discrete partitionsare used, the samples are in essence tagged or “double barcoded” whereone set of barcodes is used for identifying spatial locations and oneset of barcodes is partition-specific. In such examples, both sets ofbarcodes can be used to provide information to retain structural andmolecular context of sequence reads generated from the sample.

In some examples, the sequence information obtained from the nucleicacids provides information on intrachromosomal and/or interchromosomalinteractions between genomic loci. In further examples, the sequenceinformation includes information on chromosome conformations.

In further examples, prior to separation into the discrete partitions,the nucleic acids in the sample may be processed to link differentregions of their three dimensional structures such that regions of thesequence that are in proximity to each other within those threedimensional structures are attached to each other. As such, theseparation of the sample into discrete partitions will separate thoselinked regions into the same partition, thereby further ensuring thatthe structural context of any sequence reads from those nucleic acids isretained.

In some situations, the linking of nucleic acids may be accomplishedusing any methods known in the art used to cross-link molecules inspatial proximity. Such cross-linking agents may include withoutlimitation alkylating agents, cisplatin, nitrous oxide, psoralens,aldehydes, acrolein, glyoxal, osmium tetroxide, carbodiimide, mercuricchloride, zinc salts, picric acid, potassium dichromate, ethanol,methanol, acetone, acetic acid, and the like. In specific examples, thenucleic acids are linked using protocols designed for analysis of thethree dimensional architecture of genomes, such as the “Hi-C” protocoldescribed for example in Dekker et al., “Capturing chromosomeconformation” Science 295:1306-1311 (2002) and Berkum et al., J. Vis.Exp. (39), e1869, doi:10.3791/1869 (2010), which are each herebyincorporated by reference in its entirety for all purposes and inparticular for all teachings related to linking nucleic acid molecules.Such protocols generally involve producing a library of molecules bycrosslinking the sample so that genomic loci that are in close spatialproximity become linked. In further embodiments, the intervening DNAloop between the crosslink is digested away and then the intrasequenceregions are reverse crosslinked for addition to the library. Thedigesting and reverse crosslinking steps may occur prior to a step ofpartitioning the sample into discrete partitions, or it may occur withinthe partitions after the separating step.

In still further examples, the nucleic acids may undergo a tagging orbarcoding step that provides a common barcode for all nucleic acidswithin a partition. As will be appreciated, this barcoding may occurwith or without the nucleic acid linking/cross-linking steps discussedabove. The use of the barcoding technique disclosed herein confers theunique capability of providing individual structural and molecularcontext for genomic regions—i.e., by attributing certain sequence readsto individual sample nucleic acid molecules, and through variantcoordinated assembly, to provide a broader or even longer range inferredcontext, among multiple sample nucleic acid molecules, and/or to aspecific chromosome. The term “genomic region” or “region” as usedherein, refers to any defined length of a genome and/or chromosome. Forexample, a genomic region may refer to the association (i.e., forexample, an interaction) between more than one chromosomes. A genomicregion can also encompass a complete chromosome or a partial chromosome.In addition, a genomic region can include a specific nucleic acidsequence on a chromosome (i.e., for example, an open reading frameand/or a regulatory gene) or an intergenic noncoding region.

The use of barcoding confers the additional advantages of facilitatingthe ability to discriminate between minority constituents and majorityconstituents of the total nucleic acid population extracted from thesample, e.g. for detection and characterization of circulating tumor DNAin the bloodstream, and also reduces or eliminates amplification biasduring optional amplification steps. In addition, implementation in amicrofluidics format confers the ability to work with extremely smallsample volumes and low input quantities of DNA, as well as the abilityto rapidly process large numbers of sample partitions (droplets) tofacilitate genome-wide tagging.

In addition to providing the ability to obtain sequence information fromentire or select regions of the genome, the methods and systemsdescribed herein can also provide other characterizations of genomicmaterial, including without limitation haplotype phasing, identificationof structural variations and copy number variations, as described inU.S. Ser. Nos. 14/316,383; 14/316,398; 14/316,416; 14/316,431;14/316,447; and 14/316,463, which are herein incorporated by referencein their entirety for all purposes and in particular for all writtendescription, figures and working examples directed to characterizationof genomic material.

Generally, methods of the invention include steps as illustrated in FIG.2, which provides a schematic overview of methods of the inventiondiscussed in further detail herein. As will be appreciated, the methodoutlined in FIG. 2 is an exemplary embodiment that may be altered ormodified as needed and as described herein. As shown in FIG. 2, themethods described herein may include an optional step 201 in whichsample nucleic acids are processed to link nucleic acids in spatialproximity to each other. With or without that preliminary processingstep (201), the methods described herein will in most examples include astep in which sample nucleic acids containing are partitioned (202).Generally, each partition containing nucleic acids from genomic regionsof interest will undergo a process that results in fragments containingbarcodes (203). Those fragments may then be pooled (204) prior tosequencing (205). The sequence reads from (205) can be attributed to theoriginating structural and molecular context (206) generally due to thepartition-specific barcodes (203). Each partition may in some examplesinclude more than one nucleic acid, and will in some instances containseveral hundred nucleic acid molecules. The barcoded fragments of step203 can be generated using any methods known in the art—in someexamples, oligonucleotides are included with the samples within thedistinct partitions. Such oligonucleotides may comprise random sequencesintended to randomly prime numerous different regions of the samples, orthey may comprise a specific primer sequence targeted to prime upstreamof a targeted region of the sample. In further examples, theseoligonucleotides also contain a barcode sequence, such that thereplication process also barcodes the resultant replicated fragment ofthe original sample nucleic acid. A particularly elegant process for useof these barcode oligonucleotides in amplifying and barcoding samples isdescribed in detail in U.S. Ser. Nos. 14/316,383; 14/316,398;14/316,416; 14/316,431; 14/316,447; and 14/316,463, each of which isherein incorporated by reference in its entirety for all purposes and inparticular for all teachings related to barcoding and amplifyingoligonucleotides. Extension reaction reagents, e.g., DNA polymerase,nucleoside triphosphates, co-factors (e.g., Mg²⁺ or Mn²⁺ etc.), that arealso contained in the partitions, then extend the primer sequence usingthe sample as a template, to produce a complementary fragment to thestrand of the template to which the primer annealed, and thecomplementary fragment includes the oligonucleotide and its associatedbarcode sequence. Annealing and extension of multiple primers todifferent portions of the sample can result in a large pool ofoverlapping complementary fragments of the sample, each possessing itsown barcode sequence indicative of the partition in which it wascreated. In some cases, these complementary fragments may themselves beused as a template primed by the oligonucleotides present in thepartition to produce a complement of the complement that again, includesthe barcode sequence. In further examples, this replication process isconfigured such that when the first complement is duplicated, itproduces two complementary sequences at or near its termini to allow theformation of a hairpin structure or partial hairpin structure, whichreduces the ability of the molecule to be the basis for producingfurther iterative copies. An advantage of the methods and systemsdescribed herein is that attaching a partition- or sample-specificbarcode to the copied fragments preserves the original molecular contextof the sequenced fragments, allowing them to be attributed to theiroriginal partition and thus their originating sample nucleic acidmolecule.

Often, the sample is combined with a set of oligonucleotide tags thatare releasably-attached to beads prior to the partitioning step. Methodsfor barcoding nucleic acids are known in the art and described herein.In some examples, methods are utilized as described in Amini et al,2014, Nature Genetics, Advance Online Publication), which is hereinincorporated by reference in its entirety for all purposes and inparticular for all teachings related to attaching barcodes or otheroligonucleotide tags to nucleic acids. Methods of processing andsequencing nucleic acids in accordance with the methods and systemsdescribed in the present application are also described in furtherdetail in U.S. Ser. Nos. 14/316,383; 14/316,398; 14/316,416; 14/316,431;14/316,447; and 14/316,463 which are herein incorporated by reference intheir entirety for all purposes and in particular for all writtendescription, figures and working examples directed to processing nucleicacids and sequencing and other characterizations of genomic material.

In addition to the above workflow, targeted genomic regions may beenriched, isolated or separated, i.e., “pulled down,” for furtheranalysis, particularly sequencing, using methods that include bothchip-based and solution-based capture methods. Such methods utilizeprobes that are complementary to the genomic regions of interest or toregions near or adjacent to the genomic regions of interest. Forexample, in hybrid (or chip-based) capture, microarrays containingcapture probes (usually single-stranded oligonucleotides) with sequencesthat taken together cover the region of interest are fixed to a surface.Genomic DNA is fragmented and may further undergo processing such asend-repair to produce blunt ends and/or addition of additional featuressuch as universal priming sequences. These fragments are hybridized tothe probes on the microarray. Unhybridized fragments are washed away andthe desired fragments are eluted or otherwise processed on the surfacefor sequencing or other analysis, and thus the population of fragmentsremaining on the surface is enriched for fragments containing thetargeted regions of interest (e.g., the regions comprising the sequencescomplementary to those contained in the capture probes). The enrichedpopulation of fragments may further be amplified using any amplificationtechnologies known in the art. Exemplary methods for such targeted pulldown enrichment methods are described in U.S. Ser. No. 14/927,297, filedon Oct. 29, 2015, which is hereby incorporated by reference in itsentirety for all purposes and in particular for all teachings related totargeted pull down enrichment methods and sequencing methods, includingall written description, figures and examples. The population oftargeted genomic regions may further be enriched prior to theabove-described pull-down methods by using methods to increase coverageof those targeted regions. Such increased coverage may for example beaccomplished using targeted amplification methods, including thosedescribed for example in U.S. Ser. No. 62/119,996, filed on Feb. 24,2015, which is hereby incorporated by reference for all purposes and inparticular for all teachings related to targeted coverage of nucleicacid molecules.

In specific instances, methods described herein include a step in whichselected regions of the genome are selectively amplified prior tosequencing. This amplification, which is generally conducted usingmethods known in the art (including without limitation PCRamplification) provides at least 1×, 10×, 20×, 50×, 100×, 200×, 500×,1000×, 1500×, 2000×, 5000×, or 10000× coverage of the selected regionsof the genome, thereby providing a quantity of nucleic acids to allow denovo sequencing of those selected regions. In further embodiments, theamplification provides at least 1×-20×, 50×-100×, 200×-1000×,1500×-5000×, 5000×-10,000×, 1000×-10000×, 1500×-9000×, 2000×-8000×,2500×-7000×, 3000×-6500×, 3500×-6000×, 4000×-5500× coverage of theselected regions of the genome.

The amplification is generally conducted through extension of primerscomplementary to sequences within or near the selected regions of thegenome. In some cases, a library of primers is used that is designed totile across the regions of interest—in other words, the library ofprimers is designed to amplify regions at specific distances along theselected regions of the genome. In some instances, the selectiveamplification utilizes primers that are complementary to every 10, 15,20, 25, 50, 100, 200, 250, 500, 750, 1000, or 10000 bases along theselected regions of the genome. In still further examples, the tiledlibrary of primers is designed to capture a mixture of distances—thatmixture can be a random mixture of distances or intelligently designedsuch that specific portions or percentages of the selected regions areamplified by different primer pairs. Further information of targetedcoverage of the genome for use in accordance with methods describedherein is provided for example in U.S. Ser. No. 62/146,834, filed onApr. 13, 2015, which is hereby incorporated by reference in its entiretyfor all purposes, and in particular for all teachings related totargeted coverage of a genome.

In general, the methods and systems described herein provide nucleicacids for analyses such as sequencing. Sequencing information isobtained using methods that have the advantages of the extremely lowsequencing error rates and high throughput of short read sequencingtechnologies. As described above, the sequencing of nucleic acids istypically carried out in a manner that preserves the structural andmolecular context of sequence reads or portions of sequence reads. Bythat is meant that multiple sequence reads or multiple portions ofsequence reads may be attributable to the spatial location relative toother nucleic acids in the original sample (structural context) and tothe location of that sequence read along the linear sequence of a singleoriginating molecule of a nucleic acid (molecular context). While thissingle molecule of a nucleic acid may be of any of a variety of lengths,in preferred aspects, it will be a relatively long molecule, allowingfor preservation of long range molecular context. In particular, thesingle originating molecule is preferably substantially longer than thetypical short read sequence length, e.g., longer than 200 bases, and isoften at least 1000 bases or longer, 5000 bases or longer, 10,000 basesor longer, 20,000 bases or longer, 30,000 bases or longer, 40,000 basesor longer, 50,000 bases or longer, 60,000 bases or longer, 70,000 basesor longer, 80,000 bases or longer, 90,000 bases or longer, or 100,000bases or longer, and in some cases up to 1 megabase or longer.

As noted above, the methods and systems described herein provideindividual molecular context for short sequence reads of longer nucleicacids. As used herein, individual molecular context refers to sequencecontext beyond the specific sequence read, e.g., relation to adjacent orproximal sequences, that are not included within the sequence readitself, and as such, will typically be such that they would not beincluded in whole or in part in a short sequence read, e.g., a read ofabout 150 bases, or about 300 bases for paired reads. In particularlypreferred aspects, the methods and systems provide long range sequencecontext for short sequence reads. Such long range context includesrelationship or linkage of a given sequence read to sequence reads thatare within a distance of each other of longer than 1 kb, longer than 5kb, longer than 10 kb, longer than 15 kb, longer than 20 kb, longer than30 kb, longer than 40 kb, longer than 50 kb, longer than 60 kb, longerthan 70 kb, longer than 80 kb, longer than 90 kb or even longer than 100kb, or longer. As will be appreciated, by providing long rangeindividual molecular context, one can also derive the phasinginformation of variants within that individual molecular context, e.g.,variants on a particular long molecule will be, by definition commonlyphased.

By providing longer range individual molecular context, the methods andsystems of the invention also provide much longer inferred molecularcontext (also referred to herein as a “long virtual single moleculeread”). Sequence context, as described herein can include mapping orproviding linkage of fragments across different (generally on thekilobase scale) ranges of full genomic sequence. These methods includemapping the short sequence reads to the individual longer molecules orcontigs of linked molecules, as well as long range sequencing of largeportions of the longer individual molecules, e.g., having contiguousdetermined sequences of individual molecules where such determinedsequences are longer than 1 kb, longer than 5 kb, longer than 10 kb,longer than 15 kb, longer than 20 kb, longer than 30 kb, longer than 40kb, longer than 50 kb, longer than 60 kb, longer than 70 kb, longer than80 kb, longer than 90 kb or even longer than 100 kb. As with sequencecontext, the attribution of short sequences to longer nucleic acids,e.g., both individual long nucleic acid molecules or collections oflinked nucleic acid molecules or contigs, may include both mapping ofshort sequences against longer nucleic acid stretches to provide highlevel sequence context, as well as providing assembled sequences fromthe short sequences through these longer nucleic acids.

Furthermore, while one may utilize the long range sequence contextassociated with long individual molecules, having such long rangesequence context also allows one to infer even longer range sequencecontext. By way of one example, by providing the long range molecularcontext described above, one can identify overlapping variant portions,e.g., phased variants, translocated sequences, etc., among longsequences from different originating molecules, allowing the inferredlinkage between those molecules. Such inferred linkages or molecularcontexts are referred to herein as “inferred contigs”. In some caseswhen discussed in the context of phased sequences, the inferred contigsmay represent commonly phased sequences, e.g., where by virtue ofoverlapping phased variants, one can infer a phased contig ofsubstantially greater length than the individual originating molecules.These phased contigs are referred to herein as “phase blocks”.

By starting with longer single molecule reads (e.g., the “long virtualsingle molecule reads” discussed above), one can derive longer inferredcontigs or phase blocks than would otherwise be attainable using shortread sequencing technologies or other approaches to phased sequencing.See, e.g., published U.S. Patent Application No. 2013-0157870. Inparticular, using the methods and systems described herein, one canobtain inferred contig or phase block lengths having an N50 (where thesum of the block lengths that are greater than the stated N50 number is50% of the sum of all block lengths) of at least about 10 kb, at leastabout 20 kb, at least about 50 kb. In more preferred aspects, inferredcontig or phase block lengths having an N50 of at least about 100 kb, atleast about 150 kb, at least about 200 kb, and in many cases, at leastabout 250 kb, at least about 300 kb, at least about 350 kb, at leastabout 400 kb, and in some cases, at least about 500 kb or more, areattained. In still other cases, maximum phase block lengths in excess of200 kb, in excess of 300 kb, in excess of 400 kb, in excess of 500 kb,in excess of 1 Mb, or even in excess of 2 Mb may be obtained.

In one aspect, and in conjunction with any of the methods describedabove and later herein, the methods and systems described herein providefor the compartmentalization, depositing or partitioning of samplenucleic acids, or fragments thereof, into discrete compartments orpartitions (referred to interchangeably herein as partitions), whereeach partition maintains separation of its own contents from thecontents of other partitions. Unique identifiers, e.g., barcodes, may bepreviously, subsequently or concurrently delivered to the partitionsthat hold the compartmentalized or partitioned sample nucleic acids, inorder to allow for the later attribution of the characteristics, e.g.,nucleic acid sequence information, to the sample nucleic acids includedwithin a particular compartment, and particularly to relatively longstretches of contiguous sample nucleic acids that may be originallydeposited into the partitions. This later attribution further allowsattribution to the original structural context of those sample nucleicacids in the original sample, because nucleic acids that were close toeach other within the three dimensions of the original sample will bemore likely to be deposited into the same partition. Thus, attributionof sequence reads to the partitions (and the nucleic acids containedwithin those partitions) not only provides a molecular context as to thelinear location along the original nucleic acid molecule from which thatsequence read was derived, but also provides a structural context ofidentifying sequence reads from nucleic acids that were in close spatialproximity to each other in the three dimensional context of the originalsample.

The sample nucleic acids utilized in the methods described hereintypically represent a number of overlapping portions of the overallsample to be analyzed, e.g., an entire chromosome, exome, or other largegenomic portion. These sample nucleic acids may include whole genomes,individual chromosomes, exomes, amplicons, or any of a variety ofdifferent nucleic acids of interest. The sample nucleic acids aretypically partitioned such that the nucleic acids are present in thepartitions in relatively long fragments or stretches of contiguousnucleic acid molecules. Typically, these fragments of the sample nucleicacids may be longer than 1 kb, longer than 5 kb, longer than 10 kb,longer than 15 kb, longer than 20 kb, longer than 30 kb, longer than 40kb, longer than 50 kb, longer than 60 kb, longer than 70 kb, longer than80 kb, longer than 90 kb or even longer than 100 kb, which permits thelonger range structural and molecular context described above.

The sample nucleic acids are also typically partitioned at a levelwhereby a given partition has a very low probability of including twooverlapping fragments of a genomic locus. This is typically accomplishedby providing the sample nucleic acid at a low input amount and/orconcentration during the partitioning process. As a result, in preferredcases, a given partition may include a number of long, butnon-overlapping fragments of the starting sample nucleic acids. Thesample nucleic acids in the different partitions are then associatedwith unique identifiers, where for any given partition, nucleic acidscontained therein possess the same unique identifier, but wheredifferent partitions may include different unique identifiers. Moreover,because the partitioning step allocates the sample components into verysmall volume partitions or droplets, it will be appreciated that inorder to achieve the desired allocation as set forth above, one need notconduct substantial dilution of the sample, as would be required inhigher volume processes, e.g., in tubes, or wells of a multiwell plate.Further, because the systems described herein employ such high levels ofbarcode diversity, one can allocate diverse barcodes among highernumbers of genomic equivalents, as provided above. In particular,previously described, multiwell plate approaches (see, e.g., U.S.Published Application No. 2013-0079231 and 2013-0157870) typically onlyoperate with a hundred to a few hundred different barcode sequences, andemploy a limiting dilution process of their sample in order to be ableto attribute barcodes to different cells/nucleic acids. As such, theywill generally operate with far fewer than 100 cells, which wouldtypically provide a ratio of genomes:(barcode type) on the order of1:10, and certainly well above 1:100. The systems described herein, onthe other hand, because of the high level of barcode diversity, e.g., inexcess of 10,000, 100,000, 500,000, etc. diverse barcode types, canoperate at genome:(barcode type) ratios that are on the order of 1:50 orless, 1:100 or less, 1:1000 or less, or even smaller ratios, while alsoallowing for loading higher numbers of genomes (e.g., on the order ofgreater than 100 genomes per assay, greater than 500 genomes per assay,1000 genomes per assay, or even more) while still providing for farimproved barcode diversity per genome.

In further examples, the oligonucleotides included with the portions ofthe sample divided into the discrete partitions may comprise at least afirst and second region. The first region may be a barcode region that,as between oligonucleotides within a given partition, may besubstantially the same barcode sequence, but as between differentpartitions, may and, in most cases is a different barcode sequence. Thesecond region may be an N-mer (either a random N-mer or an N-merdesigned to target a particular sequence) that can be used to prime thenucleic acids within the sample within the partitions. In some cases,where the N-mer is designed to target a particular sequence, it may bedesigned to target a particular chromosome (e.g., chromosome 1, 13, 18,or 21), or region of a chromosome, e.g., an exome or other targetedregion. In some cases, the N-mer may be designed to target a particulargene or genetic region, such as a gene or region associated with adisease or disorder (e.g., cancer). Within the partitions, anamplification reaction may be conducted using the second N-mer to primethe nucleic acid sample at different places along the length of thenucleic acid. As a result of the amplification, each partition maycontain amplified products of the nucleic acid that are attached to anidentical or near-identical barcode, and that may represent overlapping,smaller fragments of the nucleic acids in each partition. The bar-codecan serve as a marker that signifies that a set of nucleic acidsoriginated from the same partition, and thus potentially also originatedfrom the same strand of nucleic acid. Following amplification, thenucleic acids may be pooled, sequenced, and aligned using a sequencingalgorithm. Because shorter sequence reads may, by virtue of theirassociated barcode sequences, be aligned and attributed to a single,long fragment of the sample nucleic acid, all of the identified variantson that sequence can be attributed to a single originating fragment andsingle originating chromosome. Further, by aligning multiple co-locatedvariants across multiple long fragments, one can further characterizethat chromosomal contribution. Accordingly, conclusions regarding thephasing of particular genetic variants may then be drawn, as cananalyses across long ranges of genomic sequence—for example,identification of sequence information across stretches of poorlycharacterized regions of the genome. Such information may also be usefulfor identifying haplotypes, which are generally a specified set ofgenetic variants that reside on the same nucleic acid strand or ondifferent nucleic acid strands. Copy number variations may also beidentified in this manner.

The described methods and systems provide significant advantages overcurrent nucleic acid sequencing technologies and their associated samplepreparation methods. Ensemble sample preparation and sequencing methodsare predisposed towards primarily identifying and characterizing themajority constituents in the sample, and are not designed to identifyand characterize minority constituents, e.g., genetic materialcontributed by one chromosome, from a poorly characterized or highlypolymorphic region of the genome, or material from one or a few cells,or fragmented tumor cell DNA molecule circulating in the bloodstream,that constitute a small percentage of the total DNA in the extractedsample. The methods described herein include selective amplificationmethods that increase the genetic material from these minorityconstituents, and the ability to retain the molecular context of thisgenetic material further provides genetic characterization of theseconstituents. The described methods and systems also provide asignificant advantage for detecting populations that are present withina larger sample. As such, they are particularly useful for assessinghaplotype and copy number variations—the methods disclosed herein arealso useful for providing sequence information over regions of thegenome that are poorly characterized or are poorly represented in apopulation of nucleic acid targets due to biases introduced duringsample preparation.

The use of the barcoding technique disclosed herein confers the uniquecapability of providing individual molecular context for a given set ofgenetic markers, i.e., attributing a given set of genetic markers (asopposed to a single marker) to individual sample nucleic acid molecules,and through variant coordinated assembly, to provide a broader or evenlonger range inferred individual structural and molecular context, amongmultiple sample nucleic acid molecules, and/or to a specific chromosome.These genetic markers may include specific genetic loci, e.g., variants,such as SNPs, or they may include short sequences. Furthermore, the useof barcoding confers the additional advantages of facilitating theability to discriminate between minority constituents and majorityconstituents of the total nucleic acid population extracted from thesample, e.g. for detection and characterization of circulating tumor DNAin the bloodstream, and also reduces or eliminates amplification biasduring optional amplification steps. In addition, implementation in amicrofluidics format confers the ability to work with extremely smallsample volumes and low input quantities of DNA, as well as the abilityto rapidly process large numbers of sample partitions (droplets) tofacilitate genome-wide tagging.

As described previously, an advantage of the methods and systemsdescribed herein is that they can achieve the desired results throughthe use of ubiquitously available, short read sequencing technologies.Such technologies have the advantages of being readily available andwidely dispersed within the research community, with protocols andreagent systems that are well characterized and highly effective. Theseshort read sequencing technologies include those available from, e.g.,IIlumina, Inc. (GAIIx, NextSeq, MiSeq, HiSeq, X10), Ion Torrent divisionof Thermo-Fisher (Ion Proton and Ion PGM), pyrosequencing methods, aswell as others.

Of particular advantage is that the methods and systems described hereinutilize these short read sequencing technologies and do so with theirassociated low error rates and high throughputs. In particular, themethods and systems described herein achieve the desired individualmolecular readlengths or context, as described above, but withindividual sequencing reads, excluding mate pair extensions, that areshorter than 1000 bp, shorter than 500 bp, shorter than 300 bp, shorterthan 200 bp, shorter than 150 bp or even shorter; and with sequencingerror rates for such individual molecular readlengths that are less than5%, less than 1%, less than 0.5%, less than 0.1%, less than 0.05%, lessthan 0.01%, less than 0.005%, or even less than 0.001%.

II. WORK FLOW OVERVIEW

In one exemplary aspect, the methods and systems described in thedisclosure provide for depositing or partitioning samples into discretepartitions, where each partition maintains separation of its owncontents from the contents in other partitions. As discussed in furtherdetail herein, the samples may comprise samples derived from patients,such as cell or tissue samples, which can contain nucleic acids and, incertain situations, associated proteins as well. In specific aspects,the samples used in the methods described herein include formalin fixedparaffin embedded (FFPE) cell and tissue samples and the like, as wellas any other sample types where the risk of sample degradation is high.

As used herein, the partitions refer to containers or vessels that mayinclude a variety of different forms, e.g., wells, tubes, micro ornanowells, through holes, or the like. In preferred aspects, however,the partitions are flowable within fluid streams. These vessels may becomprised of, e.g., microcapsules or micro-vesicles that have an outerbarrier surrounding an inner fluid center or core, or they may be aporous matrix that is capable of entraining and/or retaining materialswithin its matrix. In preferred aspect, however, these partitions maycomprise droplets of aqueous fluid within a non-aqueous continuousphase, e.g., an oil phase. A variety of different vessels are describedin, for example, U.S. patent application Ser. No. 13/966,150, filed Aug.13, 2013. Likewise, emulsion systems for creating stable droplets innon-aqueous or oil continuous phases are described in detail in, e.g.,Published U.S. Patent Application No. 2010-0105112. In certain cases,microfluidic channel networks are particularly suited for generatingpartitions as described herein. Examples of such microfluidic devicesinclude those described in detail in Provisional U.S. Patent ApplicationNo. 61/977,804, filed Apr. 4, 2014, the full disclosure of which isincorporated herein by reference in its entirety for all purposes.Alternative mechanisms may also be employed in the partitioning ofindividual cells, including porous membranes through which aqueousmixtures of cells are extruded into non-aqueous fluids. Such systems aregenerally available from, e.g., Nanomi, Inc.

In the case of droplets in an emulsion, partitioning of sample materialsinto discrete partitions may generally be accomplished by flowing anaqueous, sample containing stream, into a junction into which is alsoflowing a non-aqueous stream of partitioning fluid, e.g., a fluorinatedoil, such that aqueous droplets are created within the flowing streampartitioning fluid, where such droplets include the sample materials. Asdescribed below, the partitions, e.g., droplets, also typically includeco-partitioned barcode oligonucleotides. The relative amount of samplematerials within any particular partition may be adjusted by controllinga variety of different parameters of the system, including, for example,the concentration of sample in the aqueous stream, the flow rate of theaqueous stream and/or the non-aqueous stream, and the like. Thepartitions described herein are often characterized by having extremelysmall volumes. For example, in the case of droplet based partitions, thedroplets may have overall volumes that are less than 1000 pL, less than900 pL, less than 800 pL, less than 700 pL, less than 600 pL, less than500 pL, less than 400 pL, less than 300 pL, less than 200 pL, less than100 pL, less than 50 pL, less than 20 pL, less than 10 pL, or even lessthan 1 pL. Where co-partitioned with beads, it will be appreciated thatthe sample fluid volume within the partitions may be less than 90% ofthe above described volumes, less than 80%, less than 70%, less than60%, less than 50%, less than 40%, less than 30%, less than 20%, or evenless than 10% the above described volumes. In some cases, the use of lowreaction volume partitions is particularly advantageous in performingreactions with very small amounts of starting reagents, e.g., inputnucleic acids. Methods and systems for analyzing samples with low inputnucleic acids are presented in U.S. Provisional Patent Application No.62/017,580, filed Jun. 26, 2014, the full disclosure of which is herebyincorporated by reference in its entirety.

In situations involving samples that are subject to degradation and/orcontain low concentrations of components of interest, the samples may befurther processed either prior to partitioning or within the partitionsto further release the nucleic acids and/or any associated proteins forfurther analysis. For example, nucleic acids contained in FFPE samplesare generally extracted using methods known in the art. To isolatelonger nucleic acid molecules, such samples may also be processed byaddition of organocatalysts to remove formaldehyde adducts (see forexample Karmakar et al., (2015), Nature Chemistry, DOI:10.1038/NCHEM.2307, which is hereby incorporated by reference in itsentirety and in particular for all teachings related to treatment andprocessing of FFPE samples.)

Once the samples are introduced into their respective partitions thesample nucleic acids within partitions may be subjected to amplificationto increase the amount of nucleic acids for subsequent applications(such as sequencing methods described herein and known in the art). Incertain embodiments, this amplification is conducted with a library ofprimers that are directed to different parts of the genomic sequence,such that the resultant amplification products represent sequences fromsubsections of the original nucleic acid molecules. In embodiments inwhich select genomic regions are of interest, this amplification mayinclude one or more rounds of selective amplification such that regionsof the genome that are of interest for targeted coverage are present inhigher proportion in comparison to other regions of the genome(although, as will be appreciated, those other regions of the genome mayalso be amplified, but to a lesser extent, as they are not of interestfor de novo coverage). In certain embodiments, the amplificationprovides at least 1×, 2×, 5×, 10×, 20×, 30×, 40× or 50× coverage of thewhole or select regions of the genome. In further embodiments, all ofthe nucleic acids within a partition are amplified, but selected genomicregions are amplified in a targeted way such that at least 1-5, 2-10,3-15, 4-20, 5-25, 6-30, 7-35, 8-40, 9-45, or 10-50 times more ampliconsare produced from those selected genomic regions than from other partsof the genome.

Simultaneously with or subsequent to the amplification described above,the nucleic acids (or fragments thereof) within the partitions areprovided with unique identifiers such that, upon characterization ofthose nucleic acids they may be attributed as having been derived fromtheir respective origins. Accordingly, the sample nucleic acids aretypically co-partitioned with the unique identifiers (e.g., barcodesequences). In particularly preferred aspects, the unique identifiersare provided in the form of oligonucleotides that comprise nucleic acidbarcode sequences that may be attached to those samples. Theoligonucleotides are partitioned such that as between oligonucleotidesin a given partition, the nucleic acid barcode sequences containedtherein are the same, but as between different partitions, theoligonucleotides can, and preferably have differing barcode sequences.In exemplary aspects, only one nucleic acid barcode sequence will beassociated with a given partition, although in some cases, two or moredifferent barcode sequences may be present.

The nucleic acid barcode sequences will typically include from 6 toabout 20 or more nucleotides within the sequence of theoligonucleotides. These nucleotides may be completely contiguous, i.e.,in a single stretch of adjacent nucleotides, or they may be separatedinto two or more separate subsequences that are separated by one or morenucleotides. Typically, separated subsequences may typically be fromabout 4 to about 16 nucleotides in length.

The co-partitioned oligonucleotides also typically comprise otherfunctional sequences useful in the processing of the partitioned nucleicacids. These sequences include, e.g., targeted or random/universalamplification primer sequences for amplifying the genomic DNA from theindividual nucleic acids within the partitions while attaching theassociated barcode sequences, sequencing primers, hybridization orprobing sequences, e.g., for identification of presence of thesequences, or for pulling down barcoded nucleic acids, or any of anumber of other potential functional sequences. Again, co-partitioningof oligonucleotides and associated barcodes and other functionalsequences, along with sample materials is described in, for example,U.S. Ser. Nos. 14/175,935; 14/316,383; 14/316,398; 14/316,416;14/316,431; 14/316,447; and 14/316,463 which are herein incorporated byreference in their entirety for all purposes and in particular for allwritten description, figures and working examples directed to processingnucleic acids, as well as sequencing and other characterizations ofgenomic material.

Briefly, in one exemplary process, beads are provided that each mayinclude large numbers of the above described oligonucleotides releasablyattached to the beads, where all of the oligonucleotides attached to aparticular bead may include the same nucleic acid barcode sequence, butwhere a large number of diverse barcode sequences may be representedacross the population of beads used. Typically, the population of beadsmay provide a diverse barcode sequence library that may include at least1000 different barcode sequences, at least 10,000 different barcodesequences, at least 100,000 different barcode sequences, or in somecases, at least 1,000,000 different barcode sequences. Additionally,each bead may typically be provided with large numbers ofoligonucleotide molecules attached. In particular, the number ofmolecules of oligonucleotides including the barcode sequence on anindividual bead may be at least bout 10,000 oligonucleotides, at least100,000 oligonucleotide molecules, at least 1,000,000 oligonucleotidemolecules, at least 100,000,000 oligonucleotide molecules, and in somecases at least 1 billion oligonucleotide molecules.

The oligonucleotides may be releasable from the beads upon theapplication of a particular stimulus to the beads. In some cases, thestimulus may be a photo-stimulus, e.g., through cleavage of aphoto-labile linkage that may release the oligonucleotides. In somecases, a thermal stimulus may be used, where elevation of thetemperature of the beads environment may result in cleavage of a linkageor other release of the oligonucleotides form the beads. In some cases,a chemical stimulus may be used that cleaves a linkage of theoligonucleotides to the beads, or otherwise may result in release of theoligonucleotides from the beads.

In accordance with the methods and systems described herein, the beadsincluding the attached oligonucleotides may be co-partitioned with theindividual samples, such that a single bead and a single sample arecontained within an individual partition. In some cases, where singlebead partitions are desired, it may be desirable to control the relativeflow rates of the fluids such that, on average, the partitions containless than one bead per partition, in order to ensure that thosepartitions that are occupied, are primarily singly occupied. Likewise,one may wish to control the flow rate to provide that a higherpercentage of partitions are occupied, e.g., allowing for only a smallpercentage of unoccupied partitions. In preferred aspects, the flows andchannel architectures are controlled as to ensure a desired number ofsingly occupied partitions, less than a certain level of unoccupiedpartitions and less than a certain level of multiply occupiedpartitions.

FIG. 3 illustrates one particular example method for barcoding andsubsequently sequencing a sample nucleic acid. First, a samplecomprising nucleic acid may be obtained from a source, 300, and a set ofbarcoded beads may also be obtained, 310. The beads are preferablylinked to oligonucleotides containing one or more barcode sequences, aswell as a primer, such as a random N-mer or other primer. Preferably,the barcode sequences are releasable from the barcoded beads, e.g.,through cleavage of a linkage between the barcode and the bead orthrough degradation of the underlying bead to release the barcode, or acombination of the two. For example, in certain preferred aspects, thebarcoded beads can be degraded or dissolved by an agent, such as areducing agent to release the barcode sequences. In this example, a lowquantity of the sample comprising nucleic acid, 305, barcoded beads,315, and optionally other reagents, e.g., a reducing agent, 320, arecombined and subject to partitioning. By way of example, suchpartitioning may involve introducing the components to a dropletgeneration system, such as a microfluidic device, 325. With the aid ofthe microfluidic device 325, a water-in-oil emulsion 330 may be formed,wherein the emulsion contains aqueous droplets that contain samplenucleic acid, 305, reducing agent, 320, and barcoded beads, 315. Thereducing agent may dissolve or degrade the barcoded beads, therebyreleasing the oligonucleotides with the barcodes and random N-mers fromthe beads within the droplets, 335. The random N-mers may then primedifferent regions of the sample nucleic acid, resulting in amplifiedcopies of the sample after amplification, wherein each copy is taggedwith a barcode sequence, 340. Preferably, each droplet contains a set ofoligonucleotides that contain identical barcode sequences and differentrandom N-mer sequences. Subsequently, the emulsion is broken, 345 andadditional sequences (e.g., sequences that aid in particular sequencingmethods, additional barcodes, etc.) may be added, via, for example,amplification methods, 350 (e.g., PCR). Sequencing may then beperformed, 355, and an algorithm applied to interpret the sequencingdata, 360. Sequencing algorithms are generally capable, for example, ofperforming analysis of barcodes to align sequencing reads and/oridentify the sample from which a particular sequence read belongs. Inaddition, and as is described herein, these algorithms may also furtherbe used to attribute the sequences of the copies to their originatingmolecular context.

As will be appreciated, prior to or simultaneously with tagging with thebarcode sequence 340, the samples can be amplified in accordance withany of the methods described herein to provide coverage of the wholegenome or of selected regions of the genome. For embodiments in whichtargeted coverage is desired, the targeted amplification generallyresults in a larger population of amplicons representing sequences ofthe nucleic acids (or portions of thereof) in a partition containingthose selected regions of the genome as compared to amplicons from otherregions of the genome. As a result, there will be a larger number of theamplified copies containing barcode sequence 340 within a partition fromthe selected regions of the genome than from other regions of thegenome. In embodiments in which whole genome amplification is desired,the amplification may be conducted using primer libraries designed tominimize amplification biases and provide a robust level of coverageacross the entire genome.

As noted above, while single occupancy may be the most desired state, itwill be appreciated that multiply occupied partitions or unoccupiedpartitions may often be present. An example of a microfluidic channelstructure for co-partitioning samples and beads comprising barcodeoligonucleotides is schematically illustrated in FIG. 4. As shown,channel segments 402, 404, 406, 408 and 410 are provided in fluidcommunication at channel junction 412. An aqueous stream comprising theindividual samples 414 is flowed through channel segment 402 towardchannel junction 412. As described elsewhere herein, these samples maybe suspended within an aqueous fluid prior to the partitioning process.

Concurrently, an aqueous stream comprising the barcode carrying beads416 is flowed through channel segment 404 toward channel junction 412. Anon-aqueous partitioning fluid is introduced into channel junction 412from each of side channels 406 and 408, and the combined streams areflowed into outlet channel 410. Within channel junction 412, the twocombined aqueous streams from channel segments 402 and 404 are combined,and partitioned into droplets 418, that include co-partitioned samples414 and beads 416. As noted previously, by controlling the flowcharacteristics of each of the fluids combining at channel junction 412,as well as controlling the geometry of the channel junction, one canoptimize the combination and partitioning to achieve a desired occupancylevel of beads, samples or both, within the partitions 418 that aregenerated.

As will be appreciated, a number of other reagents may be co-partitionedalong with the samples and beads, including, for example, chemicalstimuli, nucleic acid extension, transcription, and/or amplificationreagents such as polymerases, reverse transcriptases, nucleosidetriphosphates or NTP analogues, primer sequences and additionalcofactors such as divalent metal ions used in such reactions, ligationreaction reagents, such as ligase enzymes and ligation sequences, dyes,labels, or other tagging reagents. The primer sequences may includerandom primer sequences or targeted PCR primers directed to amplifyingselected regions of the genome or a combination thereof.

Once co-partitioned, the oligonucleotides disposed upon the bead may beused to barcode and amplify the partitioned samples. A particularlyelegant process for use of these barcode oligonucleotides in amplifyingand barcoding samples is described in detail in U.S. Ser. Nos.14/175,935; 14/316,383; 14/316,398; 14/316,416; 14/316,431; 14/316,447;and 14/316,463, the full disclosures of which are hereby incorporated byreference in their entireties. Briefly, in one aspect, theoligonucleotides present on the beads that are co-partitioned with thesamples and released from their beads into the partition with thesamples. The oligonucleotides typically include, along with the barcodesequence, a primer sequence at its 5′ end. The primer sequence may berandom or structured. Random primer sequences are generally intended torandomly prime numerous different regions of the samples. Structuredprimer sequences can include a range of different structures includingdefined sequences targeted to prime upstream of a specific targetedregion of the sample as well as primers that have some sort of partiallydefined structure, including without limitation primers containing apercentage of specific bases (such as a percentage of GC N-mers),primers containing partially or wholly degenerate sequences, and/orprimers containing sequences that are partially random and partiallystructured in accordance with any of the description herein. As will beappreciated, any one or more of the above types of random and structuredprimers may be included in oligonucleotides in any combination.

Once released, the primer portion of the oligonucleotide can anneal to acomplementary region of the sample. Extension reaction reagents, e.g.,DNA polymerase, nucleoside triphosphates, co-factors (e.g., Mg2+ or Mn2+etc.), that are also co-partitioned with the samples and beads, thenextend the primer sequence using the sample as a template, to produce acomplementary fragment to the strand of the template to which the primerannealed, with complementary fragment includes the oligonucleotide andits associated barcode sequence. Annealing and extension of multipleprimers to different portions of the sample may result in a large poolof overlapping complementary fragments of the sample, each possessingits own barcode sequence indicative of the partition in which it wascreated. In some cases, these complementary fragments may themselves beused as a template primed by the oligonucleotides present in thepartition to produce a complement of the complement that again, includesthe barcode sequence. In some cases, this replication process isconfigured such that when the first complement is duplicated, itproduces two complementary sequences at or near its termini, to allowthe formation of a hairpin structure or partial hairpin structure, whichreduces the ability of the molecule to be the basis for producingfurther iterative copies. A schematic illustration of one example ofthis is shown in FIG. 5.

As the figure shows, oligonucleotides that include a barcode sequenceare co-partitioned in, e.g., a droplet 502 in an emulsion, along with asample nucleic acid 504. As noted elsewhere herein, the oligonucleotides508 may be provided on a bead 506 that is co-partitioned with the samplenucleic acid 504, which oligonucleotides are preferably releasable fromthe bead 506, as shown in panel A. The oligonucleotides 508 include abarcode sequence 512, in addition to one or more functional sequences,e.g., sequences 510, 514 and 516. For example, oligonucleotide 508 isshown as comprising barcode sequence 512, as well as sequence 510 thatmay function as an attachment or immobilization sequence for a givensequencing system, e.g., a P5 sequence used for attachment in flow cellsof an Illumina Hiseq or Miseq system. As shown, the oligonucleotidesalso include a primer sequence 516, which may include a random ortargeted N-mer for priming replication of portions of the sample nucleicacid 504. Also included within oligonucleotide 508 is a sequence 514which may provide a sequencing priming region, such as a “read1” or R1priming region, that is used to prime polymerase mediated, templatedirected sequencing by synthesis reactions in sequencing systems. Inmany cases, the barcode sequence 512, immobilization sequence 510 and R1sequence 514 may be common to all of the oligonucleotides attached to agiven bead. The primer sequence 516 may vary for random N-mer primers,or may be common to the oligonucleotides on a given bead for certaintargeted applications.

Based upon the presence of primer sequence 516, the oligonucleotides areable to prime the sample nucleic acid as shown in panel B, which allowsfor extension of the oligonucleotides 508 and 508 a using polymeraseenzymes and other extension reagents also co-portioned with the bead 506and sample nucleic acid 504. As shown in panel C, following extension ofthe oligonucleotides that, for random N-mer primers, would anneal tomultiple different regions of the sample nucleic acid 504; multipleoverlapping complements or fragments of the nucleic acid are created,e.g., fragments 518 and 520. Although including sequence portions thatare complementary to portions of sample nucleic acid, e.g., sequences522 and 524, these constructs are generally referred to herein ascomprising fragments of the sample nucleic acid 504, having the attachedbarcode sequences. As will be appreciated, the replicated portions ofthe template sequences as described above are often referred to hereinas “fragments” of that template sequence. Notwithstanding the foregoing,however, the term “fragment” encompasses any representation of a portionof the originating nucleic acid sequence, e.g., a template or samplenucleic acid, including those created by other mechanisms of providingportions of the template sequence, such as actual fragmentation of agiven molecule of sequence, e.g., through enzymatic, chemical ormechanical fragmentation. In preferred aspects, however, fragments of atemplate or sample nucleic acid sequence will denote replicated portionsof the underlying sequence or complements thereof.

The barcoded nucleic acid fragments may then be subjected tocharacterization, e.g., through sequence analysis, or they may befurther amplified in the process, as shown in panel D. For example,additional oligonucleotides, e.g., oligonucleotide 508 b, also releasedfrom bead 506, may prime the fragments 518 and 520. In particular,again, based upon the presence of the random N-mer primer 516 b inoligonucleotide 508 b (which in many cases will be different from otherrandom N-mers in a given partition, e.g., primer sequence 516), theoligonucleotide anneals with the fragment 518, and is extended to createa complement 526 to at least a portion of fragment 518 which includessequence 528, that comprises a duplicate of a portion of the samplenucleic acid sequence. Extension of the oligonucleotide 508 b continuesuntil it has replicated through the oligonucleotide portion 508 offragment 518. As noted elsewhere herein, and as illustrated in panel D,the oligonucleotides may be configured to prompt a stop in thereplication by the polymerase at a desired point, e.g., afterreplicating through sequences 516 and 514 of oligonucleotide 508 that isincluded within fragment 518. As described herein, this may beaccomplished by different methods, including, for example, theincorporation of different nucleotides and/or nucleotide analogues thatare not capable of being processed by the polymerase enzyme used. Forexample, this may include the inclusion of uracil containing nucleotideswithin the sequence region 512 to prevent a non-uracil tolerantpolymerase to cease replication of that region. As a result a fragment526 is created that includes the full-length oligonucleotide 508 b atone end, including the barcode sequence 512, the attachment sequence510, the R1 primer region 514, and the random N-mer sequence 516 b. Atthe other end of the sequence will be included the complement 516′ tothe random N-mer of the first oligonucleotide 508, as well as acomplement to all or a portion of the R1 sequence, shown as sequence514′. The R1 sequence 514 and its complement 514′ are then able tohybridize together to form a partial hairpin structure 528. As will beappreciated because the random N-mers differ among differentoligonucleotides, these sequences and their complements would not beexpected to participate in hairpin formation, e.g., sequence 516′, whichis the complement to random N-mer 516, would not be expected to becomplementary to random N-mer sequence 516 b. This would not be the casefor other applications, e.g., targeted primers, where the N-mers wouldbe common among oligonucleotides within a given partition. By formingthese partial hairpin structures, it allows for the removal of firstlevel duplicates of the sample sequence from further replication, e.g.,preventing iterative copying of copies. The partial hairpin structurealso provides a useful structure for subsequent processing of thecreated fragments, e.g., fragment 526.

All of the fragments from multiple different partitions may then bepooled for sequencing on high throughput sequencers as described herein.Because each fragment is coded as to its partition of origin, thesequence of that fragment may be attributed back to its origin basedupon the presence of the barcode. This is schematically illustrated inFIG. 6. As shown in one example, a nucleic acid 604 originated from afirst source 600 (e.g., individual chromosome, strand of nucleic acid,etc.) and a nucleic acid 606 derived from a different chromosome 602 orstrand of nucleic acid are each partitioned along with their own sets ofbarcode oligonucleotides as described above.

Within each partition, each nucleic acid 604 and 606 is then processedto separately provide overlapping set of second fragments of the firstfragment(s), e.g., second fragment sets 608 and 610. This processingalso provides the second fragments with a barcode sequence that is thesame for each of the second fragments derived from a particular firstfragment. As shown, the barcode sequence for second fragment set 608 isdenoted by “1” while the barcode sequence for fragment set 610 isdenoted by “2”. A diverse library of barcodes may be used todifferentially barcode large numbers of different fragment sets.However, it is not necessary for every second fragment set from adifferent first fragment to be barcoded with different barcodesequences. In fact, in many cases, multiple different first fragmentsmay be processed concurrently to include the same barcode sequence.Diverse barcode libraries are described in detail elsewhere herein.

The barcoded fragments, e.g., from fragment sets 608 and 610, may thenbe pooled for sequencing using, for example, sequence by synthesistechnologies available from IIlumina or Ion Torrent division of ThermoFisher, Inc., and the like. Once sequenced, the sequence reads from thepooled fragments 612 can be attributed to their respective fragment set,e.g., as shown in aggregated reads 614 and 616, at least in part basedupon the included barcodes, and optionally, and preferably, in partbased upon the sequence of the fragment itself. In addition, thesequence reads can be attributed to the structural context of therelative position of the nucleic acid from which those reads are derivedin relation to other nucleic acid molecules that were in close spatialproximity within the original sample. The attributed sequence reads foreach fragment set are then assembled to provide the assembled sequencefor each sample fragment, e.g., sequences 618 and 620, which in turn,may be further attributed back to their respective original chromosomesor source nucleic acid molecules (600 and 602). Methods and systems forassembling genomic sequences are described in, for example, U.S. patentapplication Ser. No. 14/752,773, filed Jun. 26, 2015, the fulldisclosure of which is hereby incorporated by reference in its entiretyand in particular for all teachings related to assembly of genomicsequences.

III. METHODS AND COMPOSITIONS FOR RETAINING STRUCTURAL CONTEXT

This disclosure provides methods, compositions and systems forcharacterization of genetic material. In general, the methods,compositions and systems described herein provide methods of analyzingcomponents of a sample while retaining information on the structural aswell as molecular context of those components as they were originally inthe sample. In other words, the description herein relation generally tospatial detection of nucleic acids in a sample, including tissue samplesthat have been or will be fixed using methods known in the art, such asformalin fixed paraffin embedded samples. As will be appreciated, any ofthe methods described in this section can be combined with any of themethods described above in the sections entitled “Overview” and“Workflow Overview” as well as with the nucleic acid sequencing methodsdescribed in subsequent sections of this specification.

In general, the methods disclosed herein relate to determining and/oranalyzing nucleic acids in a sample, including genomes, particularly theglobal genome, of a sample. The methods described herein provide theability to quantitatively or qualitatively analyze the distribution,location or expression of nucleic acid sequences (including genomicsequences) in a sample wherein the spatial context within the sample isretained. The methods disclosed herein provide an advantage overconventional methods of geographic encoding of nucleic acids in asample, because information on structural context is retained in a highthroughput processing method without requiring identification ofparticular molecular targets (such as specific genes or other nucleicacid sequences) prior to processing the sample for sequence reads. Inaddition, low amounts of nucleic acid are needed, which is particularlyadvantageous in samples such as FFPE samples in which the input nucleicacids, particularly DNA, are often fragmented or present in lowconcentrations.

Although much of the discussion herein is in terms of the analysis ofnucleic acids, it will be appreciated that the methods and systemsdiscussed herein can be adapted to apply to other components of asample, including proteins and other molecules.

As discussed above, maintaining structural context, also referred toherein as maintaining geographical context and encoding geography, meansusing methods that allow for obtaining multiple sequence reads ormultiple portions of sequence reads that can be attributed to theoriginal three-dimensional relative location of those sequence readswithin a sample. In other words, the sequence reads can be associatedwith a relative location within the sample with respect to neighboringnucleic acids (and in some situations associated proteins) in thatsample. This spatial information is available even if those neighboringnucleic acids are not physically located within the linear sequence of asingle originating nucleic acid molecule.

In general, the methods described herein include analyses in which asample containing nucleic acids is provided, where the nucleic acidscontain three dimensional structures. Portions of the sample areseparated into discrete partitions such that portions of the nucleicacid three dimensional structures are also separated into the discretepartitions—nucleic acid sequences that are in spatial proximity to eachother will tend to be separated into the same partition, thus retainingthe three-dimensional information of that spatial proximity even whenlater-obtained sequence reads are from sequences that were notoriginally on the same individual originating nucleic acid molecule.Referring to FIG. 1: if sample 101, containing nucleic acid molecules102 and 103 and 106, is separated into discrete partitions such thatsubsets of the sample are allocated into different discrete partitions,it is more likely that nucleic acid molecules 102 and 103 will be placedin the same partition with each other than with nucleic acid molecule106, because of the physical distance between nucleic acid molecule 106and 102 and 103. As such, nucleic acid molecules within the samediscrete partitions are those that were in spatial proximity to eachother in the original sample. Sequence information obtained from nucleicacids within the discrete partitions thus provides a way to analyze thenucleic acids, for example through nucleic acid sequencing, andattribute those sequence reads back to the structural context of theoriginating nucleic acid molecules.

In some examples, a library of tags is applied to the sample for spatialor geographic encoding of the sample. In certain embodiments, the tagsare oligonucleotide tags (which can include “oligonucleotide barcodes”and “DNA barcodes”), but as will be appreciated, any type of tag that iscapable of being added into a sample can be used, including withoutlimitation particles, beads, dyes, molecular inversion probes (MIPs),and the like. The library of tags can be applied to the sample throughsimple diffusion, or through active processes, such as cellularprocesses within tissue culture or cell culture samples. Cellulartransport processes include without limitation osmosis, facilitateddiffusion through the involvement of cell transport proteins, passivetransport, and active transport through the involvement of celltransport proteins and input of energy from molecules such as ATP. Ingeneral, the tags are applied such that different spatial/geographiclocations within the sample receive different tags and/or a differentconcentration of tags. Any further processing of the sample and analysisof the nucleic acids within the sample can be attributed to a particularspatial context through identification of the tags. For example,referring to FIG. 1, addition of a library of tags to sample 101 wouldresult in nucleic acids 102 and 103 having spatial proximity to adifferent portion or concentration of the library of tags than nucleicacid 106. Any further processing of the sample in accordance to theworkflows described herein would then result in nucleic acids 102 and103 being associated with the same portion/concentration of tags, andthus identification of those tags would indicate that nucleic acids 102and 103 were in spatial proximity to each other in the original sample101. Identification of nucleic acid 106 with a differentportion/concentration of tags would show that nucleic acid 106 was at adifferent spatial location than nucleic acids 102 and 103 in theoriginal sample.

In further examples, partition-specific barcodes are also employed, suchthat any sequence reads obtained can be attributed back to the partitionin which the originating nucleic acid molecules were located. Asdiscussed above, associating sequence reads to a particular partitionidentifies nucleic acid molecules that were in spatial proximity to eachother in the geography of the original sample. Further use of workflows,such as those pictured in FIG. 2, also provides information on themolecular context of the sequence reads, such that individual sequencereads can be attributed to the individual nucleic acid molecules fromwhich they originated.

To enable tagging of samples, the samples may be processed using anymethods known in the art to allow application of exogenous moleculessuch as oligonucleotide tags or other labels. For example, inembodiments in which FFPE samples are used, tags can be applied to thesamples by heating the sample to allow embedding of the tags into thesample, and then the sample could be cooled and further processed inaccordance with any of the methods described herein, including divisioninto discrete partitions and further analysis to identify sequences ofnucleic acids in the sample and the tags that are also in close spatialproximity to those sequence reads, thus retaining structural context ofthose sequence reads. Other sample processing methods include tissueprocessing methods that remove extracellular matrix and/or otherstructural impediments while retaining molecular and protein elements.Such methods include in some non-limiting examples the CLARITY method aswell as the use of other tissue clearing and labeling methods, includingthose described for example in Tomer et al., VOL. 9 NO. 7, 2014, NatureProtocols; Kebschull et al., Neuron, Volume 91 Issue 5, 7 Sep. 2016,Pages 975-987; Chung, K. et al. Structural and molecular interrogationof intact biological systems. Nature 497, 332-337 (2013); Susaki, E. A.et al. Whole-brain imaging with single-cell resolution using chemicalcocktails and computational analysis. Cell 157, 726-739 (2014); and Leeet al., ACT-PRESTO: Rapid and consistent tissue clearing and labelingmethod for 3-dimensional (3D) imaging, Scientific Reports,2016/01/11/online; Vol. 6, p. 18631, each of which is herebyincorporated by reference in its entirety for all purposes, and inparticular for any teachings related to processing samples for use instructural and molecular interrogation methods.

In certain embodiments, the methods described herein are used incombination with imaging techniques to identify spatial locations of thetags within the sample, particularly for samples that are immobilized onslides, such as FFPE samples. Such imaging techniques may allowcorrelation of sequence reads to particular locations on the slides,which allows correlation with other pathological/imaging studies thatmay have been conducted with those samples. For example, imagingtechniques may be used to provide a preliminary identification of apathology. The sequencing techniques described herein that furtherprovide sequence reads while maintaining structural context could becombined with such imaging analysis to correlate sequence reads withstructural context to corroborate or provide further information on thatpreliminary identification of the pathology. In addition, the imagingtechniques may be used in combination with tags with optical properties,such that particular tags are associated with particular regions of theimaged sample. Sequence reads that are correlated with those identifiedtags could then be further correlated with regions of the imaged sampleby virtue of their location with those tags. However, it will beappreciated that the methods described herein are independent of anysuch imaging techniques, and the ability to retain structural context isnot dependent on using an imaging technique for determining spatialinformation of nucleic acids in the sample.

In one exemplary aspect, gradients of oligonucleotides are generated ina sample to provide a coordinate system that can be decoded throughlater processing through sequencing. Such a gradient will allow taggingof cells and/or nucleic acids in the sample with an oligonucleotide oroligonucleotide concentration, which can be mapped to a physicallocation within the original sample. This coordinate system can bedeveloped by allowing a library of oligonucleotides to diffuse into asample and/or by injecting oligonucleotides into particular regions ofthe sample. When using diffusion, standard calculations of diffusionkinetics will provide a correlation between the concentration of theoligonucleotide tags and its spatial location in the original sample.Thus, any other nucleic acids identified with that concentration ofoligonucleotide tags can in turn be correlated to a particulargeographic region of the sample.

In further exemplary embodiments, the methods include processes foranalyzing nucleic acids while maintaining structural context in which alibrary of tags is applied to a sample such that different geographicalregions of the sample receive different tags. Portions of the sample,which now contain their original nucleic acids as well as the addedtags, are then separated into discrete partitions, such that portions ofthe library of tags and portions of the nucleic acids that are close toeach other in geographic location within the sample end up in the samediscrete partition. Sequencing processes, such as those described indetail herein, are used to provide sequence reads of nucleic acids inthe discrete partitions. The tags can also be identified before, afteror simultaneously with those sequencing processes. The correlation ofsequence reads to particular tags (or concentrations of tags inembodiments in which concentration gradients of tags are used) therebyhelps to provide the spatial context of the sequence reads. As discussedabove, embodiments in which the tags used for spatial encoding are usedin conjunction with partition-specific barcoding further providestructural and molecular context for the sequence reads.

IV. APPLICATIONS OF METHODS AND SYSTEMS TO NUCLEIC ACID SEQUENCING

The methods, compositions, and systems described herein are particularlyamenable for use in nucleic acid sequencing technologies. Suchsequencing technologies can include any technologies known in the art,including short-read and long-read sequencing technologies. In certainaspects, the methods, compositions and systems described herein are usedin short read, high accuracy sequencing technologies.

In general, the methods and systems described herein accomplish genomicsequencing using methods that have the advantages of the extremely lowsequencing error rates and high throughput of short read sequencingtechnologies. As described previously, an advantage of the methods andsystems described herein is that they can achieve the desired resultsthrough the use of ubiquitously available, short read sequencingtechnologies. Such technologies have the advantages of being readilyavailable and widely dispersed within the research community, withprotocols and reagent systems that are well characterized and highlyeffective. These short read sequencing technologies include thoseavailable from, e.g., Illumina, Inc. (GAIIx, NextSeq, MiSeq, HiSeq,X10), Ion Torrent division of Thermo-Fisher (Ion Proton and Ion PGM),pyrosequencing methods, as well as others.

Of particular advantage is that the methods and systems described hereinutilize these short read sequencing technologies and do so with theirassociated low error rates. In particular, the methods and systemsdescribed herein achieve the desired individual molecular readlengths orcontext, as described above, but with individual sequencing reads,excluding mate pair extensions, that are shorter than 1000 bp, shorterthan 500 bp, shorter than 300 bp, shorter than 200 bp, shorter than 150bp or even shorter; and with sequencing error rates for such individualmolecular readlengths that are less than 5%, less than 1%, less than0.5%, less than 0.1%, less than 0.05%, less than 0.01%, less than0.005%, or even less than 0.001%.

Methods of processing and sequencing nucleic acids in accordance withthe methods and systems described in the present application are alsodescribed in further detail in U.S. Ser. Nos. 14/316,383; 14/316,398;14/316,416; 14/316,431; 14/316,447; and 14/316,463 which are hereinincorporated by reference in their entirety for all purposes and inparticular for all written description, figures and working examplesdirected to processing nucleic acids and sequencing and othercharacterizations of genomic material.

In some embodiments, the methods and systems described herein forobtaining sequence information while retaining both structural andmolecular context are used for whole genome sequencing. In someembodiments, the methods described herein are used for sequencing oftargeted regions of the genome. In further embodiments, the sequencingmethods described herein include a combination of deep coverage of theselected regions with lower level linked reads across longer ranges ofthe genome. As will be appreciated, this combination of de novo andre-sequencing provides an efficient way to sequence an entire genomeand/or large portions of a genome. Targeted coverage of poorlycharacterized and/or highly polymorphic regions further provides theamount of nucleic acid material necessary for de novo sequence assembly,whereas linked genomic sequencing over other regions of the genomemaintains high throughput sequencing of the remainder of the genome. Themethods and compositions described herein are amenable to allowing forthis combination of de novo and linked read sequencing, because the samesequencing platform can be used for both types of coverage. Thepopulation of nucleic acids and/or nucleic acid fragments that aresequenced in accordance with the methods described herein can containsequences from both the genomic regions for de novo sequencing and thegenomic regions for re-sequencing.

In specific instances, methods described herein include a step in whichthe whole or selected regions of the genome are amplified prior tosequencing. This amplification, which is generally conducted usingmethods known in the art (including without limitation PCRamplification) provides at least 1×, 2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×,10×, 11×, 12×, 13×, 14×, 15×, 16×, 17×, 18×, 19×, or 20× coverage of thewhole or selected regions of the genome. In further embodiments, theamplification provides at least 1×-30×, 2×-25×, 3×-20×, 4×-15×, or5×-10× coverage of the whole or selected regions of the genome.

Amplification for coverage of the whole genome and/or select targetedregions of the genome generally conducted through extension of primerscomplementary to sequences within or near the selected regions of thegenome. In some cases, a library of primers is used that is designed totile across genomic regions of interest—in other words, the library ofprimer is designed to amplify regions at specific distances along thegenome, whether this is across selected regions or across the wholegenome. In some instances, the selective amplification utilizes primersthat are complementary to every 10, 15, 20, 25, 50, 100, 200, 250, 500,750, 1000, or 10000 bases along the selected regions of the genome. Instill further examples, the tiled library of primers is designed tocapture a mixture of distances—that mixture can be a random mixture ofdistances or intelligently designed such that specific portions orpercentages of the selected regions are amplified by different primerpairs. In further embodiments, the primer pairs are designed such thateach pair amplifies about 1-5%, 2-10%, 3-15%, 4-20%, 5-25%, 6-30%,7-35%, 8-40%, 9-45%, or 10-50% of any contiguous region of a selectedportion of the genome.

In certain embodiments and in accordance with any of the descriptionabove, the amplification occurs across a region of the genome that is atleast 3 megabasepairs long (Mb). In further embodiments, a selectedregion of the genome is selectively amplified in accordance with any ofthe methods described herein, and that selected region is at least 3.5,4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 10 Mb long. In yetfurther embodiments, the selected region of the genome is about 2-20,3-18, 4-16, 5-14, 6-12, or 7-10 Mb in length. Amplification may occuracross these regions using a single primer pair complementary tosequences at the ends or near the ends of these regions. In otherembodiments, amplification is conducted with a library of primer pairsthat are tiled across the length of the region, such that regularsegments, random segments, or some combination of different segmentdistances along the region are amplified, with the extent of coverage inaccordance with the description above.

In some embodiments, the primers used in selective amplification ofselected regions of the genome contain uracils so that the primersthemselves are not amplified.

Regardless of the sequencing platform used, in general and in accordancewith any of the methods described herein, sequencing of nucleic acids istypically carried out in a manner that preserves the structural andmolecular context of sequence reads or portions of sequence reads. Bythat is meant that multiple sequence reads or multiple portions ofsequence reads may be attributable to the relative spatial locationwithin the original sample with respect to other nucleic acids(structural context) and/or to the location within the linear sequenceof a single originating molecule of a nucleic acid (molecular context).

As will be appreciated, while the single originating molecule of anucleic acid may be of any of a variety of lengths, in preferredaspects, it will be a relatively long molecule, allowing forpreservation of long range molecular context. In particular, the singleoriginating molecule is preferably substantially longer than the typicalshort read sequence length, e.g., longer than 200 bases, and is often atleast 1000 bases or longer, 5000 bases or longer, 10,000 bases orlonger, 20,000 bases or longer, 30,000 bases or longer, 40,000 bases orlonger, 50,000 bases or longer, 60,000 bases or longer, 70,000 bases orlonger, 80,000 bases or longer, 90,000 bases or longer, or 100,000 basesor longer, and in some cases 1 megabase or longer.

Generally, methods of the invention include steps as illustrated in FIG.2, which provides a schematic overview of methods of the inventiondiscussed in further detail herein. As will be appreciated, the methodoutlined in FIG. 2 is an exemplary embodiment that may be altered ormodified as needed and as described herein.

As shown in FIG. 2, the methods described herein will in most examplesinclude a step in which samples are partitioned (202). Prior to thatpartitioning step, there may be an optional step (201) in which nucleicacids in the sample are linked to attach sequence regions that are inclose spatial proximity to each other. Generally, each partitioncontaining nucleic acids from genomic regions of interest will undergosome kind of fragmentation process and the original molecular context ofthe fragments will generally be retained (203), usually by barcoding thefragments that are specific to the partition in which they arecontained. Each partition may in some examples include more than onenucleic acid, and will in some instances contain several hundred nucleicacid molecules—in situations in which multiple nucleic acids are withina partition, any particular locus of the genome will generally berepresented by a single individual nucleic acid prior to barcoding. Asdiscussed above, barcoded fragments of step 203 can be generated usingany methods known in the art—in some examples, oligonucleotides are thesamples within the distinct partitions. Such oligonucleotides maycomprise random sequences intended to randomly prime numerous differentregions of the samples, or they may comprise a specific primer sequencetargeted to prime upstream of a targeted region of the sample. Infurther examples, these oligonucleotides also contain a barcodesequence, such that the replication process also barcodes the resultantreplicated fragment of the original sample nucleic acid. Extensionreaction reagents, e.g., DNA polymerase, nucleoside triphosphates,co-factors (e.g., Mg²⁺ or Mn²⁺ etc.), that are also contained in thepartitions, then extend the primer sequence using the sample as atemplate, to produce a complementary fragment to the strand of thetemplate to which the primer annealed, and the complementary fragmentincludes the oligonucleotide and its associated barcode sequence.Annealing and extension of multiple primers to different portions of thesample can result in a large pool of overlapping complementary fragmentsof the sample, each possessing its own barcode sequence indicative ofthe partition in which it was created. In some cases, thesecomplementary fragments may themselves be used as a template primed bythe oligonucleotides present in the partition to produce a complement ofthe complement that again, includes the barcode sequence. In furtherexamples, this replication process is configured such that when thefirst complement is duplicated, it produces two complementary sequencesat or near its termini to allow the formation of a hairpin structure orpartial hairpin structure, which reduces the ability of the molecule tobe the basis for producing further iterative copies.

Returning to the method exemplified in FIG. 2, once thepartition-specific barcodes are attached to the copied fragments, thebarcoded fragments can optionally then be pooled (204). The pooledfragments are then sequenced (205) and the sequences of the fragmentsare attributed to their originating molecular context (206), such thatthe targeted regions of interest are both identified and also linkedwith that originating molecular context. An advantage of the methods andsystems described herein is that attaching a partition- orsample-specific barcode to the copied fragments prior to enriching thefragments for targeted genomic regions preserves the original molecularcontext of those targeted regions, allowing them to be attributed totheir original partition and thus their originating sample nucleic acid.

In addition to the above workflow, targeted genomic regions may befurther enriched, isolated or separated, i.e., “pulled down,” forfurther analysis, particularly sequencing, using methods that includeboth chip-based and solution-based capture methods. Such methods utilizeprobes that are complementary to the genomic regions of interest or toregions near or adjacent to the genomic regions of interest. Forexample, in hybrid (or chip-based) capture, microarrays containingcapture probes (usually single-stranded oligonucleotides) with sequencesthat taken together cover the region of interest are fixed to a surface.Genomic DNA is fragmented and may further undergo processing such asend-repair to produce blunt ends and/or addition of additional featuressuch as universal priming sequences. These fragments are hybridized tothe probes on the microarray. Unhybridized fragments are washed away andthe desired fragments are eluted or otherwise processed on the surfacefor sequencing or other analysis, and thus the population of fragmentsremaining on the surface is enriched for fragments containing thetargeted regions of interest (e.g., the regions comprising the sequencescomplementary to those contained in the capture probes). The enrichedpopulation of fragments may further be amplified using any amplificationtechnologies known in the art. Exemplary methods for such targeted pulldown enrichment methods are described in U.S. Ser. No. 62/072,164, filedon Oct. 29, 2014, which is hereby incorporated by reference in itsentirety for all purposes and in particular for all teachings related totargeted pull down enrichment methods and sequencing methods, includingall written description, figures and examples.

In some examples, rather than whole genome sequencing, it is desirableto focus on selected regions of the genome. The methods described hereinare particularly amenable to such analyses, because the ability totarget subsets of the genome, even when those subsets are at largelinear distances but potentially in near proximity in thethree-dimensional context of the original sample, is an advantageousfeature of these methods. In some aspects, methods for coverage ofselected regions of the genome include methods in which the discretepartitions containing nucleic acid molecules and/or fragments thereoffrom those selected regions are themselves sorted for furtherprocessing. As will be appreciated, this sorting of the discretepartitions may take place in any combination with other methods ofselective amplification and/or targeted pull-down of genomic regions ofinterest described herein, in particular in any combination with thesteps of the work flow described above.

In general, methods of sorting of the discrete partitions includes stepsin which partitions containing at least a portion of the one or moreselected portions of the genome are separated from partitions that donot contain any sequences from those portions of the genome. Thesemethods include the steps of providing a population enriched forsequences of the fragments comprising at least a portion of the one ormore selected portions of the genome within the discrete partitionscontaining sequences from those portions of the genome. Such enrichmentis generally accomplished through the use of directed PCR amplificationof the fragments within the discrete partitions that include at least aportion of the one or more selected portions of the genome to produce apopulation. This directed PCR amplification thus produces ampliconscomprising at least a portion of the one or more selected portions ofthe genome. In certain embodiments, these amplicons are attached to adetectable label, which in some non-limiting embodiments may include afluorescent molecule. In general, such attachment occurs such that onlythose amplicons generated from the fragments containing the one or moreselected portions of the genome are attached to the detectable label. Insome embodiments, the attachment of the detectable labels occurs duringthe selective amplification of the one or more selected portions of thegenome. Such detectable labels may in further embodiments includewithout limitation fluorescent labels, electrochemical labels, magneticbeads, and nanoparticles. This attachment of the detectable label can beaccomplished using methods known in the art. In yet further embodiments,discrete partitions containing fragments comprising at least a portionof the one or more selected portions of the genome are sorted based onsignals emitted from the detectable labels attached to the ampliconswithin those partitions.

In further embodiments, the steps of sorting discrete partitionscontaining selected portions of the genome from those that do notcontain such sequences include the steps of (a) providing startinggenomic material; (b) distributing individual nucleic acid moleculesfrom the starting genomic material into discrete partitions such thateach discrete partition contains a first individual nucleic acidmolecule; (c) providing a population within at least some of thediscrete partitions that is enriched for sequences of the fragmentscomprising at least a portion of the one or more selected portions ofthe genome; (d) attaching a common barcode sequence to the fragmentswithin each discrete partition such that each of the fragments isattributable to the discrete partition in which it was contained; (e)separating discrete partitions containing fragments comprising at leasta portion of the one or more selected portions of the genome fromdiscrete partitions containing no fragments comprising the one or moreselected portions of the genome; (f) obtaining sequence information fromthe fragments comprising at least a portion of the one or more selectedportions of the genome, thereby sequencing one or more targeted portionsof the genomic sample while retaining molecular context. As will beappreciated, step (a) of such a method can include more than oneindividual nucleic acid molecule.

In further embodiments and in accordance with any of the above, prior toobtaining sequence information from the fragments, the discretepartitions are combined and the fragments are pooled together. Infurther embodiments, the step of obtaining sequence information from thefragments is conducted in such a way as to maintain the structural andmolecular context of the sequences of the fragments, such that theidentifying further comprises identifying fragments derived from nucleicacids located in close physical proximity within the original sampleand/or are located on the same first individual nucleic acid molecules.In still further embodiments, this obtaining of sequence informationincludes a sequencing reaction selected from the group consisting of:short read-length sequencing reactions and long read-length sequencingreactions. In yet further embodiments, the sequencing reaction is ashort read, high accuracy sequencing reaction.

In still further embodiments and in accordance with any of the above,the discrete partitions comprise droplets in an emulsion. In furtherembodiments, the barcoded fragments within the discrete partitionsrepresent about 1×-10× coverage of the one or more selected portions ofthe genome. In still further embodiments, the barcoded fragments withinthe discrete partitions represent about 2×-5× coverage of the one ormore selected portions of the genome. In yet further embodiments, thebarcoded fragments of the amplicons within the discrete partitionsrepresent at least 1× coverage of the one or more selected portions ofthe genome. In still further embodiments, the barcoded fragments withinthe discrete partitions represent at least 2× or 5× coverage of the oneor more selected portions of the genome.

In addition to providing the ability to obtain sequence information fromselected regions of the genome, the methods and systems described hereincan also provide other characterizations of genomic material, includingwithout limitation haplotype phasing, identification of structuralvariations, and identifying copy number variations, as described indetail in U.S. Ser. Nos. 14/316,383; 14/316,398; 14/316,416; 14/316,431;14/316,447; and 14/316,463 which are herein incorporated by reference intheir entirety for all purposes which are herein incorporated byreference in their entirety for all purposes and in particular for allwritten description, figures and working examples directed tocharacterization of genomic material.

In one aspect, and in conjunction with any of the methods describedabove and later herein, the methods and systems described herein providefor the compartmentalization, depositing or partitioning of samplenucleic acids, or fragments thereof, into discrete compartments orpartitions (referred to interchangeably herein as partitions), whereeach partition maintains separation of its own contents from thecontents of other partitions. Unique identifiers, e.g., barcodes, may bepreviously, subsequently or concurrently delivered to the partitionsthat hold the compartmentalized or partitioned sample nucleic acids, inorder to allow for the later attribution of the characteristics, e.g.,nucleic acid sequence information, to the sample nucleic acids includedwithin a particular compartment, and particularly to relatively longstretches of contiguous sample nucleic acids that may be originallydeposited into the partitions.

The sample nucleic acids utilized in the methods described hereintypically represent a number of overlapping portions of the overallsample to be analyzed, e.g., an entire chromosome, exome, or other largegenomic portion. These sample nucleic acids may include whole genomes,individual chromosomes, exomes, amplicons, or any of a variety ofdifferent nucleic acids of interest. The sample nucleic acids aretypically partitioned such that the nucleic acids are present in thepartitions in relatively long fragments or stretches of contiguousnucleic acid molecules. Typically, these fragments of the sample nucleicacids may be longer than 1 kb, longer than 5 kb, longer than 10 kb,longer than 15 kb, longer than 20 kb, longer than 30 kb, longer than 40kb, longer than 50 kb, longer than 60 kb, longer than 70 kb, longer than80 kb, longer than 90 kb or even longer than 100 kb, which permits thelonger range molecular context described above.

The sample nucleic acids are also typically partitioned at a levelwhereby a given partition has a very low probability of including twooverlapping fragments of the starting sample nucleic acid. This istypically accomplished by providing the sample nucleic acid at a lowinput amount and/or concentration during the partitioning process. As aresult, in preferred cases, a given partition may include a number oflong, but non-overlapping fragments of the starting sample nucleicacids. The sample nucleic acids in the different partitions are thenassociated with unique identifiers, where for any given partition,nucleic acids contained therein possess the same unique identifier, butwhere different partitions may include different unique identifiers.Moreover, because the partitioning step allocates the sample componentsinto very small volume partitions or droplets, it will be appreciatedthat in order to achieve the desired allocation as set forth above, oneneed not conduct substantial dilution of the sample, as would berequired in higher volume processes, e.g., in tubes, or wells of amultiwell plate. Further, because the systems described herein employsuch high levels of barcode diversity, one can allocate diverse barcodesamong higher numbers of genomic equivalents, as provided above. Inparticular, previously described, multiwell plate approaches (see, e.g.,U.S. Published Application No. 2013-0079231 and 2013-0157870) typicallyonly operate with a hundred to a few hundred different barcodesequences, and employ a limiting dilution process of their sample inorder to be able to attribute barcodes to different cells/nucleic acids.As such, they will generally operate with far fewer than 100 cells,which would typically provide a ratio of genomes:(barcode type) on theorder of 1:10, and certainly well above 1:100. The systems describedherein, on the other hand, because of the high level of barcodediversity, e.g., in excess of 10,000, 100,000, 500,000, 600,000, 700,000etc. diverse barcode types, can operate at genome:(barcode type) ratiosthat are on the order of 1:50 or less, 1:100 or less, 1:1000 or less, oreven smaller ratios, while also allowing for loading higher numbers ofgenomes (e.g., on the order of greater than 100 genomes per assay,greater than 500 genomes per assay, 1000 genomes per assay, or evenmore) while still providing for far improved barcode diversity pergenome.

Often, the sample is combined with a set of oligonucleotide tags thatare releasably-attached to beads prior to the partitioning step. Methodsfor barcoding nucleic acids are known in the art and described herein.In some examples, methods are utilized as described in Amini et al,2014, Nature Genetics, Advance Online Publication), which is hereinincorporated by reference in its entirety for all purposes and inparticular for all teachings related to attaching barcodes or otheroligonucleotide tags to nucleic acids. In further examples, theoligonucleotides may comprise at least a first and second region. Thefirst region may be a barcode region that, as between oligonucleotideswithin a given partition, may be substantially the same barcodesequence, but as between different partitions, may and, in most cases isa different barcode sequence. The second region may be an N-mer (eithera random N-mer or an N-mer designed to target a particular sequence)that can be used to prime the nucleic acids within the sample within thepartitions. In some cases, where the N-mer is designed to target aparticular sequence, it may be designed to target a particularchromosome (e.g., chromosome 1, 13, 18, or 21), or region of achromosome, e.g., an exome or other targeted region. As discussedherein, the N-mer may also be designed to selected regions of the genomethat tend to be poorly characterized or are highly polymorphic ordivergent from the reference sequence. In some cases, the N-mer may bedesigned to target a particular gene or genetic region, such as a geneor region associated with a disease or disorder (e.g., cancer). Withinthe partitions, an amplification reaction may be conducted using thesecond N-mer to prime the nucleic acid sample at different places alongthe length of the nucleic acid. As a result of the amplification, eachpartition may contain amplified products of the nucleic acid that areattached to an identical or near-identical barcode, and that mayrepresent overlapping, smaller fragments of the nucleic acids in eachpartition. The bar-code can serve as a marker that signifies that a setof nucleic acids originated from the same partition, and thuspotentially also originated from the same strand of nucleic acid.Following amplification, the nucleic acids may be pooled, sequenced, andaligned using a sequencing algorithm. Because shorter sequence readsmay, by virtue of their associated barcode sequences, be aligned andattributed to a single, long fragment of the sample nucleic acid, all ofthe identified variants on that sequence can be attributed to a singleoriginating fragment and single originating chromosome. Further, byaligning multiple co-located variants across multiple long fragments,one can further characterize that chromosomal contribution. Accordingly,conclusions regarding the phasing of particular genetic variants maythen be drawn, as can analyses across long ranges of genomicsequence—for example, identification of sequence information acrossstretches of poorly characterized regions of the genome. Suchinformation may also be useful for identifying haplotypes, which aregenerally a specified set of genetic variants that reside on the samenucleic acid strand or on different nucleic acid strands. Copy numbervariations may also be identified in this manner.

The described methods and systems provide significant advantages overcurrent nucleic acid sequencing technologies and their associated samplepreparation methods. Ensemble sample preparation and sequencing methodsare predisposed towards primarily identifying and characterizing themajority constituents in the sample, and are not designed to identifyand characterize minority constituents, e.g., genetic materialcontributed by one chromosome, from a poorly characterized or highlypolymorphic region of the genome, or material from one or a few cells,or fragmented tumor cell DNA molecule circulating in the bloodstream,that constitute a small percentage of the total DNA in the extractedsample. The methods described herein include selective amplificationmethods that increase the genetic material from these minorityconstituents, and the ability to retain the molecular context of thisgenetic material further provides genetic characterization of theseconstituents. The described methods and systems also provide asignificant advantage for detecting populations that are present withina larger sample. As such, they are particularly useful for assessinghaplotype and copy number variations—the methods disclosed herein arealso useful for providing sequence information for sequences that werelocated in spatial proximity to each other within the three dimensionalspace of the original sample and the original nucleic acid moleculesfrom which those sequences were derived.

The use of the barcoding technique disclosed herein confers the uniquecapability of providing individual structural and molecular context forsequences and regions of the genome. Such regions of the genome mayinclude a given set of genetic markers, i.e., attributing a given set ofgenetic markers (as opposed to a single marker) to individual samplenucleic acid molecules, and through variant coordinated assembly, toprovide a broader or even longer range inferred individual molecularcontext, among multiple sample nucleic acid molecules, and/or to aspecific chromosome. These genetic markers may include specific geneticloci, e.g., variants, such as SNPs, or they may include short sequences.Furthermore, the use of barcoding confers the additional advantages offacilitating the ability to discriminate between minority constituentsand majority constituents of the total nucleic acid population extractedfrom the sample, e.g. for detection and characterization of circulatingtumor DNA in the bloodstream, and also reduces or eliminatesamplification bias during optional amplification steps. In addition,implementation in a microfluidics format confers the ability to workwith extremely small sample volumes and low input quantities of DNA, aswell as the ability to rapidly process large numbers of samplepartitions (droplets) to facilitate genome-wide tagging.

As noted above, the methods and systems described herein provideindividual structural and molecular context for short sequence reads oflonger nucleic acids. As used herein, structural context refers to thelocation of sequences within the three dimensional space of theiroriginating nucleic acid molecules within the original sample. Asdiscussed above, although the genome is often thought of as linear,chromosomes are not rigid, and the spatial distance between two genomicloci does not necessarily correlate to their distance along thegenome—genomic regions separated by several megabases along the linearsequence may be immediately proximal to each other in three-dimensionalspace. By retaining the information of the original spatial proximity ofsequence reads, the methods and compositions described herein provide away to attribute sequence reads to long-range genomic interactions.

Similarly, the retention of individual molecular context possible withthe methods described herein provides sequence context beyond thespecific sequence read, e.g., relation to adjacent or proximalsequences, that are not included within the sequence read itself, and assuch, will typically be such that they would not be included in whole orin part in a short sequence read, e.g., a read of about 150 bases, orabout 300 bases for paired reads. In particularly preferred aspects, themethods and systems provide long range sequence context for shortsequence reads. Such long range context includes relationship or linkageof a given sequence read to sequence reads that are within a distance ofeach other of longer than 1 kb, longer than 5 kb, longer than 10 kb,longer than 15 kb, longer than 20 kb, longer than 30 kb, longer than 40kb, longer than 50 kb, longer than 60 kb, longer than 70 kb, longer than80 kb, longer than 90 kb or even longer than 100 kb, or longer. Byproviding longer range individual molecular context, the methods andsystems of the invention also provide much longer inferred molecularcontext. Sequence context, as described herein can include lowerresolution context, e.g., from mapping the short sequence reads to theindividual longer molecules or contigs of linked molecules, as well asthe higher resolution sequence context, e.g., from long range sequencingof large portions of the longer individual molecules, e.g., havingcontiguous determined sequences of individual molecules where suchdetermined sequences are longer than 1 kb, longer than 5 kb, longer than10 kb, longer than 15 kb, longer than 20 kb, longer than 30 kb, longerthan 40 kb, longer than 50 kb, longer than 60 kb, longer than 70 kb,longer than 80 kb, longer than 90 kb or even longer than 100 kb. As withsequence context, the attribution of short sequences to longer nucleicacids, e.g., both individual long nucleic acid molecules or collectionsof linked nucleic acid molecules or contigs, may include both mapping ofshort sequences against longer nucleic acid stretches to provide highlevel sequence context, as well as providing assembled sequences fromthe short sequences through these longer nucleic acids.

The methods, compositions, and systems described herein allow forcharacterization of long-range interactions across the genome as well ascharacterization of associated proteins and other molecules within asample. Like the higher-level organization of proteins, the bending andfolding of DNA and chromatin create functionally significant structuresat a wide variety of scales. At small scales, it is well known that DNAis often wound around proteins such as histones to create a structureknown as the nucleosome. These nucleosomes pack into larger ‘chromatinfibers’, and the packing pattern has been implicated as being affectedby cellular processes such as transcription. Functional structures alsoexist at larger scales: regions separated by many megabases long thelinear sequence of the genome can be immediately adjacent in3-dimensional space. Such long-range interactions between genomic locimay play a role in functional characteristics: for example, geneenhancer, silencer and insulator elements may all function across vastgenomic distances and their primary mode of action could involve adirect physical association with target genes, noncoding RNAs and/orregulatory elements. Long-range interactions are not limited to elementslocated in cis, i.e. along the same chromosome, but can also occurbetween genomic loci located in trans, i.e. on different chromosomes.The existence of long-range interactions can complicate efforts tounderstand the pathways that regulate cellular processes, because theinteracting regulatory elements could lie at a great genomic distancefrom a target gene, even on another chromosome. In the case of oncogenesand other disease-associated genes, identification of long-range geneticregulators can be of great use in identifying the genomic variantsresponsible for the disease state and the process by which the diseasestate is brought about. Thus, the ability to retain structural andmolecular context in accordance with the methods described hereinprovides a way to identify long-range genomic interactions andcharacterize any associated proteins as well.

The methods described herein are particularly useful forcharacterization of nucleic acids from an FFPE tissue sample, includinga historic FFPE tissue sample. FFPE samples generally present challengesto nucleic acid characterization, because the nucleic acids are oftenfragmented or otherwise degraded, which can limit the amount ofinformation that can be obtained using conventional methods. Thestructural and molecular context information that is retained in themethods described herein provides a unique opportunity with suchsamples, because that contextual information can providecharacterizations of long range genomic interactions even for degradedsamples, because that long-range information is accessible through shortread sequencing technologies. Applications of FFPE nucleic acidcharacterizations include comparisons of sequences from one or morehistoric samples to sequences from a sample from a subject, e.g., acancer patient to provide diagnostic or prognostic information. Forexample, the status of one or more molecular markers in a historicsample can be correlated with one or more treatment outcomes, and thecorrelation of a treatment outcome with molecular marker status in oneor more historic samples can be used to predict treatment outcomes forthe subject, e.g., a cancer patient. These predictions can be the basisfor determining whether or not to recommend a drug treatment option tothe subject.

V. SAMPLES

As will be appreciated, the methods and systems discussed herein can beused to obtain sequence information from any type of genomic material.Such genomic material may be obtained from a sample taken from apatient. Exemplary samples and types of genomic material of use in themethods and systems discussed herein include without limitationpolynucleotides, nucleic acids, oligonucleotides, circulating cell-freenucleic acid, circulating tumor cell (CTC), nucleic acid fragments,nucleotides, DNA, RNA, peptide polynucleotides, complementary DNA(cDNA), double stranded DNA (dsDNA), single stranded DNA (ssDNA),plasmid DNA, cosmid DNA, chromosomal DNA, genomic DNA (gDNA), viral DNA,bacterial DNA, mtDNA (mitochondrial DNA), ribosomal RNA, cell-free DNA,cell free fetal DNA (cffDNA), mRNA, rRNA, tRNA, nRNA, siRNA, snRNA,snoRNA, scaRNA, microRNA, dsRNA, viral RNA, and the like. In summary,the samples that are used may vary depending on the particularprocessing needs.

In particular aspects, samples of use in the present invention includeformalin fixed paraffin embedded (FFPE) cell and tissue samples and thelike, including any other sample types where the risk of sampledegradation is high. Other types of fixed samples include withoutlimitation samples that were fixed using: acrolein, glyoxal, osmiumtetroxide, carbodiimide, mercuric chloride, zinc salts, picric acid,potassium dichromate, ethanol, methanol, acetone, and/or acetic acid.

In further embodiments, the samples of use in the methods and systemsdescribed herein comprise nuclear matrix. “Nuclear matrix” refers to anycomposition comprising nucleic acids and protein. The nucleic acids maybe organized into chromosomes, wherein the proteins (i.e., for example,histones) may become associated with the chromosomes having a regulatoryfunction.

The methods and systems provided herein are particularly useful fornucleic acid sequencing applications in which the starting nucleic acids(e.g., DNA, mRNA, etc.)—or starting target nucleic acids—are present insmall quantities, or where nucleic acids that are targeted for analysis,are present at a relatively low proportion of the total nucleic acidswithin a sample. In one aspect, the present disclosure provides a methodof analyzing nucleic acids where the input nucleic acid molecules arepresent at an amount of less than 50 nanograms (ng). In furtherembodiments, the nucleic acid molecules are at an input amount of lessthan less than 40 ng. In some embodiments, the amount is less than 20ng. In some embodiments, the amount is less than 10 ng. In someembodiments, the amount is less than 5 ng. In some embodiments, theamount is less than 1 ng. In some embodiments, the amount is less than0.1 ng. Methods for isolating and analyzing nucleic acids where thestarting input amount is a small quantity are further described forexample in U.S. Ser. No. 14/752,602, filed on Jun. 26, 2015, which ishereby incorporated by reference in its entirety for all purposes and inparticular for all teachings related to isolation and characterizationof nucleic acids derived from samples in which the nucleic acids arepresent in small quantities.

As will be appreciated, samples can be processed using methods known inthe art at any point during the methods described herein. For example,samples can be processed prior to partitioning or after the sample hasbeen partitioned into discrete partitions.

In certain embodiments, the samples are processed to ensure that longernucleic acid strands are retained. In embodiments in which FFPE samplesare used, such samples may be subjected to processing to removeformaldehyde adducts to improve nucleic acid yields. Such processingmethods may include in one non-limiting example the use of water-solubleorganocatalysts to speed the reversal of formaldehyde adducts from RNAand DNA bases, as described in Karmakar et al., (2015), NatureChemistry, DOI: 10.1038/NCHEM.2307, which is hereby incorporated byreference in its entirety and in particular for all teachings related totreatment and processing of FFPE samples.

Any substance that comprises nucleic acid may be the source of a sample.The substance may be a fluid, e.g., a biological fluid. A fluidicsubstance may include, but not limited to, blood, cord blood, saliva,urine, sweat, serum, semen, vaginal fluid, gastric and digestive fluid,spinal fluid, placental fluid, cavity fluid, ocular fluid, serum, breastmilk, lymphatic fluid, or combinations thereof. The substance may besolid, for example, a biological tissue. The substance may comprisenormal healthy tissues, diseased tissues, or a mix of healthy anddiseased tissues. In some cases, the substance may comprise tumors.Tumors may be benign (non-cancer) or malignant (cancer). Non-limitingexamples of tumors may include: fibrosarcoma, myxosarcoma, liposarcoma,chondrosarcoma, osteogenic sarcoma, chordoma, angiosarcoma,endotheliosarcoma, lymphangiosarcoma, lymphangioendotheliosarcoma,synovioma, mesothelioma, Ewing's sarcoma, leiomyosarcoma,rhabdomyosarcoma, gastrointestinal system carcinomas, colon carcinoma,pancreatic cancer, breast cancer, genitourinary system carcinomas,ovarian cancer, prostate cancer, squamous cell carcinoma, basal cellcarcinoma, adenocarcinoma, sweat gland carcinoma, sebaceous glandcarcinoma, papillary carcinoma, papillary adenocarcinomas,cystadenocarcinoma, medullary carcinoma, bronchogenic carcinoma, renalcell carcinoma, hepatoma, bile duct carcinoma, choriocarcinoma,seminoma, embryonal carcinoma, Wilms' tumor, cervical cancer, endocrinesystem carcinomas, testicular tumor, lung carcinoma, small cell lungcarcinoma, non-small cell lung carcinoma, bladder carcinoma, epithelialcarcinoma, glioma, astrocytoma, medulloblastoma, craniopharyngioma,ependymoma, pinealoma, hemangioblastoma, acoustic neuroma,oligodendroglioma, meningioma, melanoma, neuroblastoma, retinoblastoma,or combinations thereof. The substance may be associated with varioustypes of organs. Non-limiting examples of organs may include brain,liver, lung, kidney, prostate, ovary, spleen, lymph node (includingtonsil), thyroid, pancreas, heart, skeletal muscle, intestine, larynx,esophagus, stomach, or combinations thereof. In some cases, thesubstance may comprise a variety of cells, including but not limited to:eukaryotic cells, prokaryotic cells, fungi cells, heart cells, lungcells, kidney cells, liver cells, pancreas cells, reproductive cells,stem cells, induced pluripotent stem cells, gastrointestinal cells,blood cells, cancer cells, bacterial cells, bacterial cells isolatedfrom a human microbiome sample, etc. In some cases, the substance maycomprise contents of a cell, such as, for example, the contents of asingle cell or the contents of multiple cells. Methods and systems foranalyzing individual cells are provided in, e.g., U.S. Ser. No.14/752,641, filed Jun. 26, 2015, the full disclosure of which is herebyincorporated by reference in its entirety.

Samples may be obtained from various subjects. A subject may be a livingsubject or a dead subject. Examples of subjects may include, but notlimited to, humans, mammals, non-human mammals, rodents, amphibians,reptiles, canines, felines, bovines, equines, goats, ovines, hens,avines, mice, rabbits, insects, slugs, microbes, bacteria, parasites, orfish. In some cases, the subject may be a patient who is having,suspected of having, or at a risk of developing a disease or disorder.In some cases, the subject may be a pregnant woman. In some case, thesubject may be a normal healthy pregnant woman. In some cases, thesubject may be a pregnant woman who is at a risking of carrying a babywith certain birth defect.

A sample may be obtained from a subject by any means known in the art.For example, a sample may be obtained from a subject through accessingthe circulatory system (e.g., intravenously or intra-arterially via asyringe or other apparatus), collecting a secreted biological sample(e.g., saliva, sputum urine, feces, etc.), surgically (e.g., biopsy)acquiring a biological sample (e.g., intra-operative samples,post-surgical samples, etc.), swabbing (e.g., buccal swab, oropharyngealswab), or pipetting.

VI. EMBODIMENTS

In some aspects, the present disclosure provides methods of analyzingnucleic acids while maintaining structural context. Such methods includethe steps of: (a) providing a sample containing nucleic acids, where thenucleic acids comprise three dimensional structures; (b) separatingportions of the sample into discrete partitions such that portions ofthe nucleic acid three dimensional structures are also separated intothe discrete partitions; (c) obtaining sequence information from thenucleic acids, thereby analyzing nucleic acids while maintainingstructural context.

In some embodiments, the sequence information from obtaining step (c)includes identification of nucleic acids that are in spatial proximityto each other.

In any embodiments, the obtaining step (c) provides information onintrachromosomal and/or interchromosomal interactions between genomicloci.

In any embodiments, the obtaining step (c) provides information onchromosome conformations.

In any embodiments, prior to separating step (b), at least some of thethree dimensional structures are processed to link different portions ofthe nucleic acids that are in proximity to each other within the threedimensional structures.

In any embodiments, the sample is a formalin-fixed paraffin sample.

In any embodiments, the nucleic acids are not isolated from the sampleprior to the separating step (b).

In any embodiments, the discrete partitions comprise beads.

In any embodiments, the beads are gel beads.

In any embodiments, prior to the obtaining step (c), the nucleic acidswithin the discrete partitions are barcoded to form a plurality ofbarcoded fragments, where fragments within a given discrete partitioneach comprise a common barcode, such that the barcodes identify nucleicacids from a given partition.

In any embodiments, the obtaining step (c) comprises a sequencingreaction selected from the group consisting of: short read-lengthsequencing reactions and long read-length sequencing reactions.

In any embodiments, the sample comprises a tumor sample.

In any embodiments, the sample comprises a mixture of tumor and normalcells.

In any embodiments, the sample comprises a nuclear matrix.

In any embodiments, the nucleic acids comprise RNA.

In any embodiments, the amount of nucleic acids in the sample is lessthan 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 ng/ml.

In some aspects, the present disclosure provides methods of analyzingnucleic acids while maintaining structural context that include thesteps of (a) forming linked nucleic acids within the sample such thatspatially adjacent nucleic acid segments are linked; (b) processing thelinked nucleic acids to produce a plurality of ligation products,wherein the ligation products contain portions of the spatially adjacentnucleic acid segments; (c) depositing the plurality of ligation productsinto discrete partitions; (d) barcoding the ligation products within thediscrete partitions to form a plurality of barcoded fragments, whereinfragments within a given discrete partition each comprise a commonbarcode, thereby associating each fragment with the linked nucleic acidfrom which it is derived; (e) obtaining sequence information from theplurality of barcoded fragments, thereby analyzing nucleic acids fromthe sample while maintaining structural context.

In further embodiments, the processing step (b) includes blunt-endligation under conditions favoring intramolecular ligation, such thatthe spatially adjacent nucleic acid segments are ligated within the samemolecule.

In any embodiments, the conditions favoring intramolecular ligationcomprise diluting the sample to reduce concentration of the nucleicacids under 10 ng/pL.

In any embodiments, the nucleic acids are not isolated from the sampleprior to the step (a).

In any embodiments, prior to step forming (a), the nucleic acids areimmunoprecipitated such that associated DNA binding proteins remainbound to the nucleic acids.

In any embodiments, the partitions comprise beads.

In any embodiments, the beads are gel beads.

In any embodiments, the sample comprises a tumor sample.

In any embodiments, the sample comprises a mixture of tumor and normalcells.

In any embodiments, the processing step includes reversal of the linkingsubsequent to forming the ligation products.

In any embodiments, the obtaining step (e) provides information onintrachromosomal and/or interchromosomal interactions between genomicloci.

In any embodiments, the obtaining step (e) provides information onchromosome conformations.

In any embodiments, the chromosome conformations are associated withdisease states.

In any embodiments, the processing step results in ligation productscomprising nucleic acids that were originally in close spatial proximityin the sample.

In any embodiments, the obtaining step (e) comprises a sequencingreaction selected from the group consisting of: short read-lengthsequencing reactions and long read-length sequencing reactions.

In any embodiments, the sequencing reaction is a short read, highaccuracy sequencing reaction.

In any embodiments, the forming step (a) includes cross-linking nucleicacids in the sample.

In any embodiments, the forming step (a) results in covalent linksbetween spatially adjacent nucleic acid segments.

In some aspects, the present disclosure provides methods of analyzingnucleic acids while maintaining structural context that include thesteps of: (a) forming linked nucleic acids within the sample such thatspatially adjacent nucleic acid segments are linked; (b) depositing thelinked nucleic acids into discrete partitions; (c) processing the linkednucleic acids to produce a plurality of ligation products, wherein theligation products contain portions of the spatially adjacent nucleicacid segments; (d) barcoding the ligation products within the discretepartitions to form a plurality of barcoded fragments, wherein fragmentswithin a given discrete partition each comprise a common barcode,thereby associating each fragment with the linked nucleic acid fromwhich it is derived; (e) obtaining sequence information from theplurality of barcoded fragments, thereby analyzing nucleic acids fromthe sample while maintaining structural context.

In further embodiments, the processing step (c) includes blunt-endligation under conditions favoring intramolecular ligation, such thatthe spatially adjacent nucleic acid segments are ligated within the samemolecule.

In any embodiments, the sample is a formalin-fixed paraffin sample.

In any embodiments, the sample comprises a nuclear matrix.

In any embodiments, the nucleic acids comprise RNA.

In any embodiments, the nucleic acids are not isolated from the sampleprior to step (a).

In any embodiments, prior to the forming step (a), the nucleic acids areimmunoprecipitated such that associated DNA binding proteins remainbound to the nucleic acids.

In any embodiments, the partitions comprise beads.

In any embodiments, the beads are gel beads.

In any embodiments, the sample comprises a tumor sample.

In any embodiments, the sample comprises a mixture of tumor and normalcells.

In any embodiments, the processing step (c) results in ligation productscomprising nucleic acids that were originally in close spatial proximityin the sample.

In any embodiments, the obtaining step (e) provides information onintrachromosomal and/or interchromosomal interactions between genomicloci.

In any embodiments, the obtaining step (e) comprises a sequencingreaction selected from the group consisting of: short read-lengthsequencing reactions and long read-length sequencing reactions.

In any embodiments, the sequencing reaction is a short read, highaccuracy sequencing reaction.

In some aspects, the present disclosure provides methods of analyzingnucleic acids while maintaining structural context that include thesteps of (a) cross-linking nucleic acids within the sample to formcross-linked nucleic acids, wherein the cross-linking forms covalentlinks between spatially adjacent nucleic acid segments; (b) depositingthe cross-linked nucleic acids into discrete partitions; (c) processingthe cross-linked nucleic acids to produce a plurality of ligationproducts, wherein the ligation products contain portions of thespatially adjacent nucleic acid segments; (d) obtaining sequenceinformation from the plurality of ligation products, thereby analyzingnucleic acids from the sample while maintaining structural context.

In further embodiments the processing step (b) includes blunt-endligation under conditions favoring intramolecular ligation, such thatthe spatially adjacent nucleic acid segments are ligated within the samemolecule.

In any embodiments, the sample is a formalin-fixed paraffin sample.

In any embodiments, the sample comprises a nuclear matrix.

In any embodiments, the nucleic acids comprise RNA.

In any embodiments, the nucleic acids are not isolated from the sampleprior to the cross-linking step (a).

In any embodiments, the amount of nucleic acids in the sample is lessthan 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 ng/ml.

In any embodiments, prior to the cross-linking step (a), the nucleicacids are immunoprecipitated such that associated DNA binding proteinsremain bound to the nucleic acids.

In any embodiments, prior to the obtaining step (d), the ligationproducts are associated with a barcode.

In any embodiments, ligation products within the same partition receivecommon barcodes, such that the barcodes identify ligation products froma given partition.

In any embodiments, the obtaining step (d) comprises a sequencingreaction selected from the group consisting of: short read-lengthsequencing reactions and long read-length sequencing reactions.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

EXAMPLES Example 1 Sample Preparation

Sample preparation methods were modified to provide long DNA moleculesfrom FFPE samples. FIG. 7 illustrates an exemplary workflow, withmodifications indicated for preparing FFPE samples for both whole genomesequencing (WGS) and whole exome sequencing (WES). For example, afterDNA extraction, a standard thermalcycling protocol was modified at 701to move the 98 degree denaturation step from the end of each cycle tothe beginning. In addition, a 70 degree hold was added for 2 minutes atthe end of each cycle.

During the post cycling cleanup 702 and the WES library preparation andtarget enrichments steps 704 and 705, 1.8X Solid Phase ReversibleImmobilisation (SPRI) beads over normal protocols were used.

Another modification included changing conditions during the shearingstep 703, in which an ultrasonicator with a peak incident power of about450 was used, as opposed to a standard sonicator with a peak incidentpower of 50.

An additional modification that may be used in certain situations is tofirst process the FFPE sample with organocatalysts in order to removeformaldehyde adducts, as for example described in Karmakar et al.,(2015), Nature Chemistry, DOI: 10.1038/NCHEM.2307. Such protocolsinclude adding 5 mM organocatalysts in 30 mM pH 7 Tris buffer to thesamples to effect adduct reversal. Effective organocatalysts includewithout limitation water-soluble bifunctional catalysts, such as theanthranilate and phosphanilate catalysts described in Karmakar et al.Reversal of the adducts has the effect of improving the yield of nucleicacid yields from the sample.

Example 2 Barcodinq of FFPE Samples

FFPE samples (which can include FFPE samples on a slide) can be taggedwith DNA barcodes applied in spatially well-defined pattern, such asthose used in DNA microarray printing. The DNA barcode (henceforthcalled barcode-1) is either long so that it will not diffuse out insubsequent steps or is covalently applied to the FFPE sample. To enablebarcoding DNA to get embedded into FFPE slide, the sample is heated, andthen the barcodes are added. The barcodes are generally a library ofbarcodes such that different barcodes are provided in different parts ofthe slide. The barcodes may also be added in different concentrations indifferent parts of the slide to assist in the geographic encoding—inthat situation, the library of barcodes may comprise identical ordifferent barcodes. After the barcodes are added, the slide is thencooled and then separated into portions generally through cutting inways such as using laser microdissection, mechanical/acoustic means, andthe like. Fluorophores or Qdots may also be used instead of barcodes,however, barcoding enables massively parallel random encapsulation ofsample portions while retaining local spatial information (e.g., tumorvs normal cells).

The portions of samples containing the barcodes can then be put in asequencing system, including a droplet based system such as the 10×Genomics Chromium™ system, such that a single barcoded portion isencapsulated per droplet.

Deparaffinization of the sample can be carried out in the droplet byheating. Paraffin is immiscible in water but soluble in certain oils andthus the paraffin can be easily removed from the droplet upon heatingthe droplets on-chip. Xylene could also be used in a liquid-liquidextraction process to de-paraffinize the sample portions and ready theirnucleic acid contents for further processing.

Further steps include de-cross-linking methylene bridges of thedeparaffinized sample. For this step, specialized chemical means can beused to remove the crosslinks and thereby enable access to the containednucleic acids for any subsequent processing, including the nucleic acidbarcoding, amplification, and library preparation steps discussed herein(see for example FIG. 2). Note that the spatial barcoding DNA is alsoencapsulated in the droplet. The second barcoding step of the individualnucleic acids will serve to barcode the nucleic acids and the barcodeused to spatially encode the sample. Sequence reads can then be stitchedtogether to provide information that can then be compared to theoriginal spatial location in the sample and hence related topathological data.

In alternative versions of this spatial encoding workflow, thede-cross-linking step is first performed within the droplet and then thenucleic acids in the sample, including genomic DNA as well as thespatial encoding barcodes, are attached to particles or are otherwiseisolated from the sample. The nucleic acids are then re-encapsulated andsubjected to the workflow of barcoding and sequencing in methodsdescribed herein, including that pictured in FIG. 2.

The present specification provides a complete description of themethodologies, systems and/or structures and uses thereof in exampleaspects of the presently-described technology. Although various aspectsof this technology have been described above with a certain degree ofparticularity, or with reference to one or more individual aspects,those skilled in the art could make numerous alterations to thedisclosed aspects without departing from the spirit or scope of thetechnology hereof. Since many aspects can be made without departing fromthe spirit and scope of the presently described technology, theappropriate scope resides in the claims hereinafter appended. Otheraspects are therefore contemplated. Furthermore, it should be understoodthat any operations may be performed in any order, unless explicitlyclaimed otherwise or a specific order is inherently necessitated by theclaim language. It is intended that all matter contained in the abovedescription and shown in the accompanying drawings shall be interpretedas illustrative only of particular aspects and are not limiting to theembodiments shown. Unless otherwise clear from the context or expresslystated, any concentration values provided herein are generally given interms of admixture values or percentages without regard to anyconversion that occurs upon or following addition of the particularcomponent of the mixture. To the extent not already expresslyincorporated herein, all published references and patent documentsreferred to in this disclosure are incorporated herein by reference intheir entirety for all purposes. Changes in detail or structure may bemade without departing from the basic elements of the present technologyas defined in the following claims.

What is claimed:
 1. A method of analyzing nucleic acids from a formalinfixed paraffin embedded (FFPE) sample while maintaining structuralcontext of nucleic acids within the sample, the method comprising: (a)forming linked nucleic acids within the FFPE sample such that spatiallyadjacent nucleic acid segments are linked; (b) processing the linkednucleic acids to produce a plurality of ligation products, wherein theligation products contain portions of the spatially adjacent nucleicacid segments; (c) depositing individual portions of the FFPE sampleinto discrete partitions, wherein each individual portion of the FFPEsample comprises one or more of the ligation products; (d) barcoding theligation products within the discrete partitions to form a plurality ofbarcoded fragments, wherein fragments within a given discrete partitioneach comprise a common barcode, thereby associating each fragment withthe linked nucleic acid from which it is derived; (e) obtaining sequenceinformation from the plurality of barcoded fragments, thereby analyzingnucleic acids from the sample while maintaining structural context. 2.The method of claim 1, wherein the processing step (b) includesblunt-end ligation under conditions favoring intramolecular ligation,such that the spatially adjacent nucleic acid segments are ligatedwithin the same molecule.
 3. The method of claim 2, wherein theconditions favoring intramolecular ligation comprise diluting the sampleto reduce concentration of the nucleic acids under 10 ng/μL.
 4. Themethod of claim 1, wherein the sample comprises a nuclear matrix.
 5. Themethod of claim 1, wherein the nucleic acids comprise RNA.
 6. The methodof claim 1, wherein the amount of nucleic acids in the sample is lessthan 50 ng/ml.
 7. The method of claim 1, wherein the partitions comprisebeads.
 8. The method of claim 7, wherein the beads are gel beads.
 9. Themethod of claim 1, wherein the sample comprises a tumor sample.
 10. Themethod of claim 1, wherein the sample comprises a mixture of tumor andnormal cells.
 11. The method of claim 1, wherein the processing stepincludes reversal of the linking subsequent to forming the ligationproducts.
 12. The method of claim 1, wherein the obtaining step (e)provides information on intrachromosomal and/or interchromosomalinteractions between genomic loci.
 13. The method of claim 1, whereinthe obtaining step (e) provides information on chromosome conformations.14. The method of claim 13, wherein the chromosome conformations areassociated with disease states.
 15. The method of claim 1, wherein theprocessing step results in ligation products comprising nucleic acidsthat were originally in close spatial proximity in the sample.
 16. Themethod of claim 1, wherein the obtaining step (e) comprises a sequencingreaction selected from the group consisting of: short read-lengthsequencing reactions and long read-length sequencing reactions.
 17. Themethod of claim 16, wherein the sequencing reaction is a short read,high accuracy sequencing reaction.
 18. The method of claim 1, whereinthe forming step (a) comprises cross-linking nucleic acids in thesample.
 19. The method of claim 1, wherein the forming step (a) resultsin covalent links between spatially adjacent nucleic acid segments. 20.A method of analyzing nucleic acids from a formalin fixed paraffinembedded (FFPE) sample while maintaining structural context of nucleicacids within the sample, the method comprising: (a) forming linkednucleic acids within the FFPE sample such that spatially adjacentnucleic acid segments are linked; (b) depositing individual portions ofthe FFPE sample into discrete partitions, wherein each individualportion of the FFPE sample comprises one or more linked nucleic acids;(c) processing the linked nucleic acids to produce a plurality ofligation products, wherein the ligation products contain portions of thespatially adjacent nucleic acid segments; (d) barcoding the ligationproducts within the discrete partitions to form a plurality of barcodedfragments, wherein fragments within a given discrete partition eachcomprise a common barcode, thereby associating each fragment with thelinked nucleic acid from which it is derived; (e) obtaining sequenceinformation from the plurality of barcoded fragments, thereby analyzingnucleic acids from the sample while maintaining structural context. 21.The method of claim 20, wherein the processing step (c) includesblunt-end ligation under conditions favoring intramolecular ligation,such that the spatially adjacent nucleic acid segments are ligatedwithin the same molecule.
 22. The method of claim 20, wherein the samplecomprises a nuclear matrix.
 23. The method of claim 20, wherein thenucleic acids comprise RNA.
 24. The method of claim 20, wherein thepartitions comprise beads.
 25. The method of claim 24, wherein the beadsare gel beads.
 26. The method of claim 20, wherein the sample comprisesa tumor sample.
 27. The method of claim 20, wherein the sample comprisesa mixture of tumor and normal cells.
 28. The method of claim 20, whereinthe processing step (c) results in ligation products comprising nucleicacids that were originally in close spatial proximity in the sample. 29.The method of claim 20, wherein the obtaining step (e) providesinformation on intrachromosomal and/or interchromosomal interactionsbetween genomic loci.
 30. The method of claim 20, wherein the obtainingstep (e) comprises a sequencing reaction selected from the groupconsisting of: short read-length sequencing reactions and longread-length sequencing reactions.
 31. The method of claim 30, whereinthe sequencing reaction is a short read, high accuracy sequencingreaction.